Estimating Domestic Self-Supplied Water Use in Rhode Island, 2014–21

Scientific Investigations Report 2024-5109
Prepared in cooperation with the Rhode Island Water Resources Board
By: , and 

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Acknowledgments

Kathleen Crawley and Patrick Killian of the Rhode Island Water Resources Board provided useful feedback to the direction of the project. Andrew Murray (U.S. Environmental Protection Agency) and Joshua Larsen (U.S. Geological Survey) provided peer reviews of this report. The authors appreciate the feedback of the following U. S. Geological Survey employees for technical review: Joe Ayotte, Luther Schalk, Paul Barlow, Rob Dudley, and Laura Medalie, who also assisted with project development.

Abstract

Water withdrawal from private groundwater wells is often unaccounted for in water planning studies, and water from private wells can be a source of exposure to environmental contaminants. The sizes of populations that depend on private wells for domestic water use and the amounts of water that are withdrawn from these wells are generally poorly represented in data collection efforts because of the challenges of locating, metering, or gathering withdrawal information from individual property owners. To address this problem, the U.S. Geological Survey, in cooperation with the Rhode Island Water Resources Board, estimated the volume of water withdrawn from domestic self-supply wells and the populations who use them for the State of Rhode Island at a 30-meter pixel spatial resolution and one-month temporal resolution between July 2014 and June 2021.

The number of people reliant on domestic self-supply wells has increased in Rhode Island over the study period; however, the statewide estimate of total water withdrawal has not statistically increased. Withdrawals from private wells are largest in the inland areas of the western part of the State, and the towns of Scituate and Charlestown have the highest estimated withdrawals. Statewide monthly withdrawals ranged from 3.987 million gallons per day in March 2018 to 7.767 million gallons per day in September 2016. The median per capita domestic water use rate was 46.0 gallons per capita per day.

Introduction

Water for domestic use in the United States generally comes from either public water systems (PWSs) or private groundwater wells (domestic self-supply wells). Domestic water use includes water for indoor and outdoor household purposes, such as drinking, cleaning, cooking, bathing, and watering lawns and home gardens. Nationally, about 87 percent of the population is served by PWSs (Dieter and others, 2018). PWSs are generally more efficient than self-supply wells in terms of providing clean and treated water but require investment in physical infrastructure and have higher operation costs. In rural areas, investment requirements for public supply become much greater relative to the number of people served. Thus, the proportion of houses dependent on domestic self-supply wells tends to decrease as housing density increases (Johnson and others, 2019). The northeastern United States has the highest population density in the country, yet even in this region sizeable portions of the population rely on self-supply wells. Rhode Island has the second highest population density in the United States, and as much as 10 percent of the population is estimated to use self-supply wells (Johnson and others, 2022). Fifty-one percent of all estimated water withdrawals in Rhode Island in 2015 were for domestic use: 6.6 million gallons per day (Mgal/d) were from self-supply wells and 56 Mgal/d were deliveries from PWSs, out of total withdrawals of 122 Mgal/d (Dieter and others, 2018).

An understanding of which populations use self-supply wells is important for managing water resources and assessing risk from various environmental contaminants. Domestic self-supply wells may be pathways through which populations are exposed to environmental and anthropogenic contaminants, such as arsenic, uranium, pesticides, fertilizers, and hydrocarbons (Bulka and others, 2022; DeSimone and others, 2014; Lombard and others, 2021; Soriano and others, 2022). Many well owners are unaware of the risk of possible exposure through self-supply wells because these wells are not frequently tested for contaminants that do not affect the taste or clarity of the water. Additionally, withdrawals from domestic self-supply wells (or any wells) may affect, or be affected by, changes in groundwater levels from drought or competing uses (Jasechko and Perrone, 2021; Mullaney, 2004). Though withdrawals from self-supply wells represent a relatively small percentage of total domestic water use in the United States (Dieter and others, 2018), in aggregate they may be a substantial part of overall water resources available in rural areas. Furthermore, because self-supply wells are commonly shallower than public-supply wells, they are more likely to be vulnerable to declines in water-table levels and contamination than public supply wells (DeSimone and others, 2014).

Despite their importance, determining the locations of domestic self-supply wells remains a challenge. Domestic self-supply wells are largely unregulated and are not subject to the reporting requirements placed on PWSs by State and Federal Government organizations (Bowen and others, 2019). Between 1960 and 1990, household water source was reported on the long-form decennial census questionnaire, but this questionnaire was only sent to a subset of the population (one in five households in 1990), and the question about household water source was removed after 1990. Many studies still use the results of the 1990 decennial census to estimate populations who use domestic self-supply wells (Wild and Nimiroski, 2007; Johnson and Belitz, 2017; Murray and others, 2021). A snapshot of county- and State-level estimates of total domestic water use (self-supplied water withdrawals and deliveries from PWSs) for 2015 is available in Dieter and others (2018); however, we are not aware of studies that estimate domestic self-supplied water withdrawals statewide at a greater spatial resolution than counties for any State other than Maine (Ryan P. Gordon, Amber H. Whittaker, and Robert G. Marvinney, Maine Geological Survey, written commun., 2021).

The Rhode Island Water Resources Board (RIWRB) is an agency charged with managing the use and conservation of water throughout the State, including ensuring sufficient water supplies (Rhode Island General Assembly, 1956). As such, this agency has been working to amass comprehensive withdrawal information throughout Rhode Island, which is entered into the Water Use Needs, Data, and Reporting (WUNDR) database created by the RIWRB in collaboration with the University of Rhode Island and the Rhode Island Geological Survey (Rhode Island Water Resources Board, 2022). This database enables users to visualize and download water withdrawal and use information at the subwatershed scale, each of which is assigned a 12-digit hydrologic unit code (HUC12). Deliveries to domestic water users from large and small PWSs have been quantified through reporting (large PWSs report annually to the RIWRB) or through previous investigations (domestic use estimates for small PWSs were the subject of a previous study; Kathleen Crawley, RIWRB, written commun., 2022); however, withdrawals from domestic self-supply wells are not accounted for in these data. In order to provide comprehensive domestic water-use in Rhode Island, the U.S. Geological Survey, in cooperation with the RIWRB, generated data that provide estimates of the amounts of water withdrawn from domestic self-supply wells and the populations who use them (Chamberlin and Armstrong, 2024).

Purpose and Scope

The purpose of this report is to (1) provide estimates of the population served by PWSs and domestic self-supply wells in Rhode Island and (2) provide estimates of the amount of domestic self-supplied water use in Rhode Island. Seasonal population estimates for winter (January 1 to March 31 and October 1 to December 31) and summer (April 1 to September 30) and monthly domestic self-supplied water withdrawal estimates from July 2014 to June 2021 are provided as 30-meter (m) pixel raster datasets that can be aggregated to any level of interest for Rhode Island (Chamberlin and Armstrong, 2024). Results in this report are presented at scales of municipality and subwatershed (HUC12).

Data and Methods

Estimates of populations served by public supply and domestic self-supply wells were generated by updating published population information for the State of Rhode Island and by using the spatial boundaries of PWS service areas to partition the population into areas that are served by public-supply or self-supply wells. Daily per capita domestic water use rates calculated from reported PWS water-use data were combined with the updated population estimates to generate estimates of water withdrawals from domestic self-supply wells.

Population Rasters

Seasonal (summer and winter) statewide dasymetric population rasters were created by following methodology developed for Maine (Ryan P. Gordon, Amber H. Whittaker, and Robert G. Marvinney, Maine Geological Survey, written commun., 2021). Dasymetric maps reorganize map data from a collection unit (such as a census block group) into more precise areas using additional information (such as land cover; Baynes and others, 2022). Briefly stated, this method was applied to update populations from a 2010 national dasymetric raster (U.S. Environmental Protection Agency, 2016) for each season from 2014 to 2021 on the basis of U.S. Census Bureau American Community Survey 5-year (ACS5) estimates. All U.S. Census Bureau data for this project were acquired through the National Historic Geographic Information System supported by IPUMS (Manson and others, 2023).

The base 2010 national dasymetric raster was clipped to the State of Rhode Island (figs. 1 and 2). The base 2010 national dasymetric raster (U.S. Environmental Protection Agency, 2016) was generated by using the 2011 National Land Cover Database release (Homer and others, 2015) and the 2010 U.S. Census Bureau decennial census (Manson and others, 2023). The product attributed the populations reported in the 2010 decennial census for each census block group to 30-m pixels of developed land from the National Land Cover Database, as well as some additional processing that is detailed in U.S. Environmental Protection Agency (2016). Population changes were calculated for each year at the census block group level as the percent change in population between the 2010 decennial census count (on which the U.S. Environmental Protection Agency dasymetric raster was based) and the ACS5 population estimates for 2014–19 and 2021. For 2020, the estimates were taken from the 2020 decennial census count. The block group boundaries were static between 2010 and 2019, and no adjustments were made for these years. Block group boundaries were redrawn, however, for the 2020 census: some block groups were merged or split, and the boundaries of others were altered. Because the base population map was generated from the 2010 census boundaries, we remapped the 2020 and 2021 census populations to 2010 census boundaries. Using the published nationwide relationship files for 2020 and 2010 block groups (U.S. Census Bureau, 2023), we divided the 2020 boundary population values into each area of overlapping land area by assuming population was evenly distributed across land area and then recombined values on the basis of the 2010 block group associations. Block groups in Rhode Island had a median land area of 0.88 square kilometer in 2010 and 0.94 square kilometer in 2020.

A map of Rhode Island showing locations of towns and waterbodies mentioned in the
                        text.
Figure 1.

Map showing the study area, which encompasses the State of Rhode Island. The study area excludes adjacent water bodies within the State borders, such as Narragansett Bay and Block Island Sound.

Population per 30-meter pixel ranges from 0.01 to 608.73.
Figure 2.

Map showing the U.S. Environmental Protection Agency 2010 dasymetric raster plotted for Rhode Island. Data from U.S. Environmental Protection Agency (2016).

Block group population estimates from the ACS5 are published yearly, but they represent the average of the 5 years leading up to the publication year. A similar product, the U.S. Census Bureau American Communities Survey 1-year (ACS1; Manson and others, 2023) was used to adjust for the 5-year averaging. The ACS1 population estimates represent the value for the reported year only; however, these estimates have a great amount of error at small spatial scales, making them unsuitable for use at subcounty scales. The ACS1 population estimates of larger areas, such as States, are more robust. To adjust the block group population estimates for the 5-year averaging in the ACS5 data, the statewide sum of each yearly dasymetric raster was compared with the published ACS1 population of Rhode Island. Then, each pixel was multiplied by a coefficient C for each year y, described as

Cy=Pyi=1ndi, y 
,
(1)
where

P

represents the published ACS1 population for Rhode Island in year y,

d

represents the population of the dasymetric raster for pixel i and year y, and

n

is the number of pixels in the dasymetric raster of Rhode Island.

This equation adjusts the total statewide population of the dasymetric rasters to be equal to the published ACS1 statewide population, while preserving the spatial distributions of populations described by the ACS5 data.

Many parts of Rhode Island, such as the coastlines of southern Rhode Island, are popular summer tourist destinations, which affects the seasonal population of these areas. For each block group, we based the amount of the seasonal population variation on ASC5 estimates (and decennial census count values for 2020) of the fraction of housing units that are classified as “vacant for seasonal recreational use.” Using the yearly dasymetric rasters as the baseline population, we assumed that the size of households vacant for seasonal recreational use were the same as the year-round households and calculated the summer population estimates for each pixel as

PS=PW1+ HVHO
,
(2)
where

PS

is the summer population of a pixel,

PW

is the winter population of a pixel,

HV

is the number of seasonally vacant housing units in the census block group intersecting with a pixel, and

HO

is the number of occupied housing units.

After discussion with experts at the RIWRB with knowledge of seasonal tourism in Rhode Island, seasonal adjustments were applied to create summer population estimates, and year-round population estimates from the U.S. Census Bureau were used for winter population estimates (Kathleen Crawley, RIWRB, oral commun., 2022).

Public Water System Boundaries

Domestic self-supply wells were assumed to be the source of water in areas of the State outside the boundaries of PWS service areas. For this analysis, boundaries for all PWS service areas in Rhode Island were used, including community (serving primarily domestic water users) and noncommunity (which may provide water for other uses as well, such as schools or businesses) boundaries. All areas within Rhode Island that were outside of PWS boundaries were assumed to be served by domestic self-supply wells. To obtain geospatial boundaries of the service areas of PWSs, we used different methods for large (defined as >50 million gallons per year) and small (defined as <50 million gallons per year and >10 connections) systems.

The boundaries of 28 large PWS service areas were obtained from the Rhode Island Geographic Information System (2022). Adjustments were made to account for the mergers of two PWSs (East Smithfield Water District and Johnston Water Control Facilities) with a larger PWS (Providence Water) during the study period (East Smithfield in 2017 and Johnston in 2020). A PWS boundary shapefile that represented 1995 system boundaries (Kathleen Crawley, RIWRB, written commun., 2020) provided historical boundaries that were used to separate the district of Johnston Water Control Facilities from Providence Water for 2014–19, and the East Smithfield Water District from Providence Water for 2014–16.

The boundaries of the small community and noncommunity PWS service areas were generated manually for this project. A list of 416 small providers in the Rhode Island Safe Drinking Water Information System (SDWIS; maintained by the Rhode Island Department of Health and accessible through the Rhode Island Drinking Water Viewer; Rhode Island Department of Health, 2024) was obtained in 2020. Metadata in SDWIS was first used to identify the general service area of a PWS; then, more precise boundaries of service areas were estimated on a building-by-building basis. Geospatial boundaries were manually drawn around clusters of buildings assumed to be within the service area for each small provider.

Service areas of large PWSs make up 50 percent of the area of Rhode Island. Service areas of the small PWSs are estimated to be 1 percent of the area of the State. The large PWSs are concentrated around the Narragansett Bay, where population density is highest (figs. 2 and 3). Small PWSs are primarily scattered throughout the western half of the State, though they can also be found on islands in the Narragansett Bay, within pockets surrounded by large PWSs, and in other parts of the State (fig. 3).

Large public water suppliers are concentrated around Narragansett Bay. Small suppliers
                        are primarily scattered throughout the western half of the state.
Figure 3.

Map of public water systems in Rhode Island in 2022. Service area boundaries from Rhode Island Geographic Information System (2022) and this study.

Per Capita Rates of Water Use

Daily per capita domestic water use was calculated from available water-use data of selected PWSs throughout the State. Nineteen systems were selected on the basis of the completeness and availability of monthly residential water sales or withdrawal data for both seasons. Additional criteria for selection of representative PWSs were that (1) they were in operation in 2010 and would therefore be represented by the base 2010 dasymetric raster (U.S. Environmental Protection Agency, 2016), (2) the seasonality of reported water use matched expected patterns for domestic water use (higher in summer than winter), and (3) the calculated daily per capita residential water use coefficients did not greatly exceed those reported for domestic use in Dieter and others (2018), here defined as being >200 gallons per capita per day (gpcd). Water retail sales data for 10 large PWSs were obtained from annual reports submitted to the RIWRB. These systems serve a variety of customer types, but only the sales to residential customers (including both single and multi-family customers) were used because these were assumed to represent domestic water use. Metered water withdrawal data for the small systems were provided by an engineering firm overseeing many water systems to RIWRB, and the 9 small systems used in this study represent systems serving exclusively residential communities. Therefore, water withdrawal was assumed to represent domestic water use in these systems. The 19 selected systems are highlighted in figure 3.

To calculate per capita rates of domestic water use, data on volumes of withdrawals (for the 9 small systems) or water sales (for the 10 large systems) were converted to per capita rates by using computed estimates of the population served for each system (described in the report section “Population Served by Public Supply and Self-Supply Wells”). These per capita water use rates were applied to areas of domestic self-supply on the basis of physical nearness by using the simplifying assumption that water-use behavior might vary across parts of the State but does not vary between domestic water users regardless of whether the source of water is a public-supply or self-supply well.

Water Volumes Withdrawn or Sold

The RIWRB collects annual reports from all large PWSs each year, which includes monthly residential water-use sales by volume (Kathleen Crawley, RIWRB, written commun., 2020). Monthly residential data were compiled for 10 large PWSs from July 2014 to June 2021. Initial quality assurance and quality control included checking that sales data remained within the same order of magnitude across a time series; values outside of these criteria were investigated for errors in reporting units. Monthly values that appeared to be outliers or that were missing were flagged, and the RIWRB contacted the individual PWS to resolve flagged data. No efforts were made to fill gaps in a time series if the RIWRB was unable to obtain records or corrections from the suppliers. The monthly data for each system were then converted to mean daily water use volumes according to the number of days in each month.

Small PWSs are not required to submit annual reports to the RIWRB. However, an engineering firm that operates dozens of small PWSs in the State provided metered information for nine small community (residential) suppliers (Kathleen Crawley, RIWRB, written commun. 2022). For these systems, volume per day was calculated as the change in total metered volume divided by the number of days between meter readings. We excluded periods between meter reads that were greater than 6 months because this exceeded the seasonal resolution of our population estimates. In several instances, the engineering firm that provided these data had adjusted the volume per day measurements on the basis of knowledge of their operations (for example, meter replacements or recalibrations); these changes were incorporated into our study. If a single system withdrew water from multiple wells, the volume per day withdrawals from the wells were summed to get a systemwide total. The daily withdrawals were averaged over each month.

Population Estimates

For the 10 large PWSs, reported populations served were obtained from the annual reports submitted to the RIWRB. Annual reports are generally reported for fiscal years (defined as the 12-month period from July 1 to June 30 and designated by the calendar year in which it ends), and we therefore used the end of one fiscal year and the beginning of the next as the time step for year-to-year population changes when comparing these annual report values with recalculated population-served values described in the report section “Population Served by Public-Supply and Self-Supply Wells.” The methods used to estimate populations served that are reported to the RIWRB varied widely among suppliers, from values based on the number of service connections to values based on professional estimates of tourist activity (Kathleen Crawley, RIWRB, written commun. 2023).

For small PWSs, reported populations served were obtained from metadata in the SDWIS and from a report that summarized small PWS populations served in Rhode Island (Kathleen Crawley, RIWRB, written commun. 2022). SDWIS population-served estimates are generated by the Rhode Island Department of Health using methodology that differs from methods used for the large PWSs.

Owing to the variation in methodology of estimates of reported populations served, for consistency, we recalculated populations served for all large and small PWSs using the boundary polygons for each PWS and the population dasymetric rasters created for each season in this study. The per capita rates of water use were calculated by using our recalculated population-served values.

For all PWSs, recalculated populations served were derived from summer and winter dasymetric rasters for each year, and from the spatial polygons of system service-area boundaries. Populations served were calculated by summing raster pixel values within the polygons using the terra package in R (Hijmans, 2023). Small PWSs are required to register with SDWIS if they serve an average of at least 25 people for at least 60 days per year or have at least 15 service connections. Therefore, we adjusted any recalculated populations served of fewer than 25 people to 25 people.

Water-Withdrawal Calculations

Water withdrawal in gallons per day was calculated for each pixel as the product of population per pixel and the per capita water-use rate in gallons per person per day. Per capita water-use rates from the supplier data were applied across the State using nearest neighbor assignments. Differences in per capita water-use rates between suppliers were considered to be representative of regional water use, incorporating variations in water use on the basis of variations in weather patterns, land use, and socioeconomics across the State. For each month, the State was divided into Voronoi polygons surrounding suppliers who had reported data for the given month. Voronoi polygons depict areas of the State that are spatially closest to each of these suppliers (fig. 4). The Voronoi polygons were converted to rasters at the same resolution as the seasonal dasymetric rasters. For each fiscal year, the total withdrawal for each pixel (in Mgal/d) was calculated as a weighted average of the monthly rasters (also in Mgal/d), weighted by the number of days in each month.

Values of gallons per capita per day range from 18.53 to 78.50, and the state is divided
                        into 18 polygons.
Figure 4.

Map showing Voronoi polygons of daily per capita domestic water use rate coefficients in Rhode Island for January 2020. Public water system service boundaries that the daily per capita domestic water use rates were calculated from are overlain for reference. Data from Rhode Island Geographic Information System (2022).

Results

All spatial results of this study are generated as 30-m monthly rasters (Chamberlin and Armstrong, 2024) that can be used as input for further applications by any interested parties. This report summarizes results by municipality and subwatershed (HUC12).

Population Change Rasters

Population in Rhode Island has generally been increasing since 2010; however, increases are not consistent across the State. In 2020, 98.7 percent of block groups had population change coefficients between −1 and 1 (unitless), with a median change of 0.04 (fig. 5). Block groups along the coastline, on Block Island, and along Narragansett Bay generally had the highest seasonality coefficients, sometimes exceeding 2 (a doubling of population in the summer), indicating the highest variability between summer and winter populations (fig. 6). Statewide in 2020, 79 percent of block groups had seasonality coefficients of 1 (meaning there were no vacant seasonal units in the block group), and 98.9 percent of block groups had seasonality coefficients less than 2.

Population change coefficients range from -0.920 to 16.450. The largest changes are
                        in block groups around the Narragansett Bay.
Figure 5.

Map showing population change coefficients for block groups in Rhode Island between 2010 and 2020. Data from Chamberlin and Armstrong (2024).

Seasonal coefficients range from 1 to 98.00. The largest changes are in the southern
                        half of the state, including Block Island.
Figure 6.

Map showing seasonal scaling coefficients for block groups in Rhode Island in 2020. Winter is defined as January 1 to March 31 and October 1 to December 31; summer is defined as April 1 to September 30. Data from Chamberlin and Armstrong (2024).

Population Served by Public Supply and Self-Supply Wells

Our recalculated estimates of population served by each PWS generally agreed with reported values (Kendall’s τ = 0.78; fig. 7). This association was stronger for the larger suppliers (Kendall’s τ = 0.89) than for the smaller suppliers (Kendall’s τ = 0.39). For large PWSs, the median difference between values was 6.6 percent of the reported population values, whereas for small suppliers the median difference was 27 percent of the reported value. This difference was largely driven by smaller reported populations for the small districts (median reported population of 170 people; Kathleen Crawley, RIWRB, written commun., 2020) than for the large districts (median reported population of 40,000 people; Kathleen Crawley, RIWRB, written commun., 2020; Rhode Island Department of Health, 2024). There was little bias overall (percent bias = 0.8 percent); however, the recalculated population-served estimates for the small PWSs were biased low compared with the reported population-served estimates (percent bias = −46.8 percent). We found that the recalculated population served by a PWS increased over time for large PWSs (seasonal Mann-Kendall, p < 0.001, Sen slope = 1,591 people per month; fig. 8) but did not change significantly over time for small PWSs (seasonal Mann-Kendall, p = 0.46).

Much of the change for large PWSs occurred between 2019 and 2020. Population served by large PWSs was lowest in October–December 2014 (934,295 people), and highest in April–September 2020 (1,004,405 people). Over the timeframe of this study, a median of 20,440 people were served by small PWSs in winter, and a median of 21,961 people were served in summer (fig. 8). Estimates of the statewide population served by domestic self-supply wells increased over fiscal years 2015–21 (seasonal Mann-Kendall, p = 0.01, Sen slope = 253 people per month; fig. 8). Much of this increase occurred between 2019 and 2020, and Rhode Island reported an increase in population that year of 3.5 percent (Manson and others, 2023). Though 2020 data came from the decennial census and 2019 data came from the American Community Survey, the increase continued in 2021, which also used data from the American Community Survey. This increase was exaggerated in some locations, such as in the two block groups on Block Island, which together had a 54 percent increase in reported population from 2019 to 2020 (916 people to 1,410 people); however, reported population decreased in 2021 to 1,007 people. As Block Island has a large number of seasonally vacant units (1,444 units out of 1,947 total units in 2020; Manson and others, 2023), this population increase was even greater in the summer using our methodology.

Values plot mostly on-top of the line of 1:1 equivalency, though some values plot
                        below the line.
Figure 7.

Graph showing recalculated population-served estimates of public water supply systems in Rhode Island for 2014–21 (y-axis) plotted against the reported population-served estimates (x-axis).

All three plots show large population increases in 2020.
Figure 8.

Graphs showing total populations in Rhode Island served by A, large public water systems reporting to the Rhode Island Water Resources Board (RIWRB); B, domestic self-supply wells; and C, small public water systems not reporting to the RIWRB. Data from Chamberlin and Armstrong (2024).

Populations who relied on self-supply wells varied spatially: the largest populations of self-supply well users were in the towns of Charlestown, Glocester, Scituate, Burrillville, and North Smithfield (table 1) and in the drainage basins of Branch River, Woonasquatucket River, Moswansicut Pond-Huntinghouse Brook, Upper Wood River, and Tomaquag Brook-Pawcatuck River1 (table 2; Moswansicut Pond, Huntinghouse Brook, and Tomaquag Brook not shown on any map). The largest differences between summer and winter populations who use domestic self-supply wells were seen in the towns of Charlestown, Glocester, Little Compton, New Shoreham, and South Kingstown. Populations who use domestic self-supply wells are available in Chamberlin and Armstrong (2024) and can be aggregated to other spatial resolutions as well.

1

HUC12s 010900030204, 010900040502, 010900040604, 010900050101, and 010900050205.

Table 1.    

Populations who use domestic self-supply wells in Rhode Island by municipality for calendar years 2014–2021.

[Data from Chamberlin and Armstrong (2024). Winter is defined as January 1 to March 31 and October 1 to December 31; summer is defined as April 1 to September 30.]

Table 1.    Populations who use domestic self-supply wells in Rhode Island by municipality for calendar years 2014–2021.
Barrington Summer 78 80 76 79 77 74 79 88
Winter 77 79 76 76 75 72 76 85
Bristol Summer 1,784 1,919 2,004 2,087 2,148 2,190 1,602 1,986
Winter 1,765 1,902 1,987 2,077 2,147 2,182 1,593 1,974
Burrillville Summer 8,522 8,244 8,088 8,254 8,291 8,750 8,470 8,478
Winter 8,379 8,107 7,883 8,038 8,035 8,227 8,087 8,059
Central Falls Summer 0 0 0 0 0 0 0 0
Winter 0 0 0 0 0 0 0 0
Charlestown Summer 9,606 10,036 10,017 9,954 10,238 10,139 10,227 10,152
Winter 7,053 7,028 6,999 7,022 7,024 7,012 7,210 7,214
Coventry Summer 7,640 7,641 7,323 7,158 7,208 7,370 7,559 7,880
Winter 7,453 7,435 7,096 6,990 6,928 7,123 7,326 7,717
Cranston Summer 1,616 1,633 1,626 1,604 1,481 1,458 1,731 1,683
Winter 1,599 1,633 1,620 1,598 1,476 1,453 1,726 1,683
Cumberland Summer 1,138 1,121 1,156 1,086 1,051 931 1,235 912
Winter 1,136 1,085 1,113 1,044 1,016 909 1,235 912
East Greenwich Summer 947 889 952 937 1,001 929 944 944
Winter 926 870 936 917 982 929 884 883
East Providence Summer 37 39 39 37 35 33 38 40
Winter 37 39 39 37 35 33 38 40
Exeter Summer 6,154 6,104 6,136 6,292 6,353 6,173 6,031 6,331
Winter 6,118 6,104 6,136 6,166 6,202 6,043 5,864 6,243
Foster Summer 4,554 4,578 4,574 4,605 4,587 4,595 4,352 4,403
Winter 4,532 4,558 4,556 4,585 4,565 4,595 4,352 4,403
Glocester Summer 9,049 9,348 9,486 9,498 9,693 9,863 9,813 9,996
Winter 8,880 9,017 9,055 9,093 9,291 9,399 9,142 9,253
Hopkinton Summer 7,797 7,852 7,928 7,730 7,868 7,978 8,216 8,207
Winter 7,495 7,509 7,510 7,520 7,505 7,530 7,738 7,782
Jamestown Summer 3,476 3,343 3,352 3,191 3,251 2,997 3,379 3,797
Winter 2,742 2,702 2,902 2,771 2,979 2,880 2,898 3,093
Johnston Summer 1,463 1,744 1,579 1,496 1,486 1,467 1,536 1,666
Winter 1,463 1,744 1,579 1,496 1,486 1,467 1,536 1,666
Lincoln Summer 66 68 71 64 70 65 77 78
Winter 66 68 71 64 70 65 77 78
Little Compton Summer 4,747 4,790 4,713 4,814 4,794 4,916 5,057 5,079
Winter 3,439 3,455 3,443 3,473 3,448 3,435 3,554 3,536
Middletown Summer 2,183 2,020 1,859 1,814 1,695 1,614 1,882 1,594
Winter 2,053 1,840 1,730 1,592 1,429 1,327 1,466 1,285
Narragansett Summer 63 63 82 84 85 86 52 53
Winter 49 45 57 56 55 57 40 38
New Shoreham Summer 2,329 2,302 2,168 2,187 2,216 2,305 7,016 2,454
Winter 531 536 525 494 483 535 851 601
Newport Summer 132 120 138 169 136 158 255 202
Winter 63 38 40 47 53 56 136 110
North Kingstown Summer 1,163 1,163 1,143 1,175 1,174 1,185 1,303 1,360
Winter 1,108 1,117 1,098 1,132 1,134 1,136 1,247 1,293
North Providence Summer 0 0 0 0 0 0 0 0
Winter 0 0 0 0 0 0 0 0
North Smithfield Summer 7,822 7,882 7,739 7,871 7,836 7,868 8,051 8,376
Winter 7,739 7,864 7,718 7,804 7,764 7,820 7,988 8,305
Pawtucket Summer 0 0 0 0 0 0 0 0
Winter 0 0 0 0 0 0 0 0
Portsmouth Summer 567 494 517 520 520 517 700 682
Winter 490 420 455 465 463 453 629 620
Providence Summer 5 5 5 5 5 4 4 4
Winter 5 5 5 5 5 4 4 4
Richmond Summer 6,706 6,659 6,618 6,647 6,686 6,710 6,950 7,122
Winter 6,502 6,504 6,516 6,539 6,554 6,603 6,832 6,946
Scituate Summer 9,065 9,110 9,080 9,245 9,170 9,170 8,953 9,021
Winter 9,043 9,089 9,080 9,165 9,085 9,065 8,888 8,921
Smithfield Summer 3,188 3,136 3,159 3,184 3,185 3,166 3,454 3,546
Winter 3,185 3,133 3,159 3,184 3,185 3,165 3,454 3,546
South Kingstown Summer 3,081 3,152 3,330 3,376 3,636 3,645 4,132 4,000
Winter 2,663 2,725 2,896 2,881 3,083 3,084 3,356 3,203
Tiverton Summer 5,520 5,569 5,463 5,399 5,340 5,288 5,957 5,381
Winter 5,136 5,119 5,078 4,998 4,933 4,896 5,232 4,806
Warren Summer 500 457 443 463 460 466 494 508
Winter 459 425 415 429 429 436 480 477
Warwick Summer 859 767 932 900 640 709 844 1,074
Winter 857 764 929 897 638 707 843 1,073
West Greenwich Summer 4,629 4,490 4,508 4,479 4,295 4,205 4,326 4,253
Winter 4,628 4,489 4,506 4,477 4,291 4,204 4,326 4,253
West Warwick Summer 75 72 80 81 85 81 86 78
Winter 75 69 77 77 80 77 85 77
Westerly Summer 470 507 533 564 530 507 511 623
Winter 435 459 490 511 477 447 455 555
Woonsocket Summer 8 7 7 7 8 8 8 8
Winter 8 7 7 7 8 8 8 8
Rhode Island Summer 117,044 117,409 116,925 117,057 117,337 117,625 125,323 122,059
Winter 108,192 107,985 107,781 107,729 107,419 107,435 109,658 110,745
Table 1.    Populations who use domestic self-supply wells in Rhode Island by municipality for calendar years 2014–2021.

Table 2.    

Populations who use domestic self-supply wells in Rhode Island by 12-digit hydrologic unit code (HUC12) subwatershed for calendar years 2014–2021.

[Data from Chamberlin and Armstrong (2024). HUC12s from U.S. Geological Survey (2020), accessed with nhdplusTools (Blodgett and Johnson, 2023). Map labels correspond to labels on figure 10. Winter is defined as January 1 to March 31 and October 1 to December 31; summer is defined as April 1 to September 30. —, no data]

Table 2.    Populations who use domestic self-supply wells in Rhode Island by 12-digit hydrologic unit code (HUC12) subwatershed for calendar years 2014–2021.
1 Westport River 010900020502 12 Winter 1,989 1,930 1,930 1,870 1,735 1,770 2,028 1,791
Summer 2,095 2,046 2,041 1,991 1,803 1,843 2,215 1,944
2 Cold Brook-Rhode Island Sound 010900020503 77 Winter 2,352 2,344 2,350 2,376 2,341 2,373 2,433 2,561
Summer 3,404 3,402 3,370 3,442 3,401 3,538 3,396 3,589
3 Clear River 010900030202 75 Winter 4,602 4,468 4,303 4,508 4,335 4,306 4,098 4,741
Summer 4,708 4,595 4,485 4,700 4,569 4,736 4,421 5,098
4 Chepachet River 010900030203 100 Winter 4,355 4,223 4,402 4,360 4,260 4,353 4,361 3,923
Summer 4,388 4,265 4,466 4,429 4,321 4,398 4,384 3,923
5 Branch River 010900030204 98 Winter 7,190 7,108 6,944 6,776 6,934 7,161 7,469 7,253
Summer 7,261 7,112 6,972 6,835 6,991 7,250 7,548 7,337
6 Mill River 010900030205 2 Winter 0 0 0 0 0 0 0 0
Summer 0 0 0 0 0 0 0 0
7 Emerson Brook-Blackstone River 010900030206 28 Winter 2,153 2,357 2,330 2,415 2,377 2,489 2,380 2,291
Summer 2,168 2,365 2,340 2,426 2,388 2,490 2,383 2,296
8 Abbott Run 010900030207 58 Winter 680 650 646 614 616 573 706 585
Summer 682 666 665 633 632 582 706 585
9 Peters River-Blackstone River 010900030208 75 Winter 1,249 1,225 1,230 1,195 1,176 1,133 1,403 1,267
Summer 1,255 1,250 1,260 1,227 1,207 1,150 1,413 1,279
10 Ten Mile River 010900040401 12 Winter 0 0 0 0 0 0 0 0
Summer 0 0 0 0 0 0 0 0
11 Moshassuck River 010900040501 100 Winter 110 117 124 115 131 147 168 222
Summer 110 117 124 115 131 147 168 222
12 Woonasquatucket River 010900040502 100 Winter 6,377 6,529 6,336 6,387 6,292 6,273 6,612 6,942
Summer 6,414 6,637 6,445 6,482 6,429 6,398 6,882 7,272
13 Big River 010900040601 100 Winter 2,267 2,243 2,148 2,280 2,105 2,101 2,316 2,230
Summer 2,282 2,269 2,168 2,301 2,133 2,125 2,328 2,238
14 Flat River Reservoir 010900040602 100 Winter 5,399 5,441 5,248 5,222 5,257 5,397 5,542 5,722
Summer 5,571 5,614 5,452 5,371 5,502 5,613 5,745 5,853
15 South Branch Pawtuxet River 010900040603 100 Winter 3 3 3 3 4 4 4 4
Summer 3 3 3 3 4 4 4 5
16 Moswansicut Pond-Huntinghouse Brook 010900040604 100 Winter 5,622 5,697 5,411 5,629 5,518 5,102 5,055 5,052
Summer 5,655 5,789 5,502 5,778 5,707 5,286 5,317 5,393
17 Barden Reservoir-Ponaganset River 010900040605 100 Winter 3,714 3,789 3,735 3,509 3,887 3,756 3,492 3,585
Summer 3,753 3,830 3,802 3,584 3,935 3,841 3,567 3,656
18 Scituate Reservoir 010900040606 100 Winter 4,146 4,354 4,391 4,439 4,394 4,626 4,399 4,454
Summer 4,162 4,370 4,391 4,439 4,394 4,626 4,399 4,454
19 North Branch Pawtuxet River 010900040607 100 Winter 1,756 1,688 1,753 1,728 1,841 1,963 2,042 2,063
Summer 1,763 1,690 1,755 1,731 1,844 1,982 2,052 2,079
20 Pocasset River 010900040608 100 Winter 198 226 233 219 212 205 220 220
Summer 198 226 233 219 212 205 220 220
21 Pawtuxet River 010900040609 100 Winter 1,135 1,158 1,142 1,143 1,048 1,034 1,172 1,147
Summer 1,144 1,159 1,149 1,151 1,054 1,040 1,178 1,148
22 Palmer River 010900040701 6 Winter 81 69 55 55 47 45 58 69
Summer 81 75 59 60 52 49 58 69
23 Barrington River-Warren River 010900040702 51 Winter 70 73 71 71 71 66 71 79
Summer 71 74 71 73 72 68 73 82
24 Quequechan River 010900040803 2 Winter 1,655 1,614 1,546 1,482 1,452 1,414 1,611 1,543
Summer 1,712 1,663 1,583 1,524 1,509 1,469 1,763 1,689
25 Seekonk River-Providence River 010900040901 81 Winter 57 58 57 56 53 51 58 58
Summer 57 59 58 57 54 51 58 58
26 Old Mill Creek-Narragansett Bay 010900040902 40 Winter 77 75 81 83 71 79 75 80
Summer 87 84 90 88 73 85 81 87
27 Greenwich Bay 010900040903 85 Winter 818 723 887 856 599 670 802 1,038
Summer 818 725 888 856 600 671 802 1,038
28 Hunt River 010900040904 100 Winter 1,257 1,206 1,262 1,247 1,303 1,248 1,265 1,213
Summer 1,281 1,234 1,288 1,276 1,333 1,259 1,327 1,276
29 Mount Hope Bay 010900040905 21 Winter 2,028 2,154 2,231 2,338 2,428 2,461 1,913 2,270
Summer 2,072 2,184 2,258 2,371 2,455 2,488 1,928 2,302
30 Upper West Passage 010900040906 30 Winter 36 32 31 31 30 32 38 33
Summer 61 59 60 51 52 51 57 46
31 Upper East Passage 010900040907 53 Winter 353 290 319 318 325 315 510 497
Summer 399 330 351 348 351 347 554 541
32 Lower West Passage 010900040908 61 Winter 2,029 2,098 2,358 2,375 2,538 2,451 2,282 2,071
Summer 2,400 2,476 2,626 2,667 2,800 2,560 2,693 2,635
33 Lower East Passage 010900040909 36 Winter 1,805 1,478 1,339 1,190 1,124 1,155 1,369 1,694
Summer 2,247 1,833 1,626 1,445 1,221 1,275 1,561 1,927
34 Sakonnet River 010900040910 66 Winter 3,830 3,915 3,890 3,833 3,892 3,673 3,768 3,401
Summer 4,432 4,655 4,502 4,563 4,728 4,545 5,109 4,502
35 Aquidneck Island-Frontal Atlantic Ocean 010900040911 99 Winter 29 31 32 32 33 31 40 39
Summer 30 32 34 33 33 31 40 39
36 Pettaquamscutt River-Frontal Atlantic Ocean 010900040912 99 Winter 557 543 548 561 571 571 625 677
Summer 608 582 594 604 609 615 679 736
37 Upper Wood River 010900050101 86 Winter 5,956 5,926 5,863 5,391 5,279 5,120 5,344 4,992
Summer 6,075 6,029 5,975 5,532 5,519 5,313 5,559 5,134
38 Lower Wood River 010900050102 95 Winter 3,479 3,570 3,633 3,610 3,573 3,595 3,629 3,438
Summer 3,579 3,686 3,757 3,643 3,764 3,744 3,825 3,618
39 Chipuxet River-Pawcatuck River 010900050201 100 Winter 1,248 1,299 1,322 1,355 1,317 1,429 1,394 1,461
Summer 1,253 1,304 1,330 1,363 1,338 1,453 1,419 1,484
40 Usquepaug River 010900050202 100 Winter 4,714 4,580 4,779 4,978 5,161 5,080 4,833 5,527
Summer 4,782 4,611 4,816 5,017 5,243 5,160 4,919 5,640
41 Beaver River 010900050203 100 Winter 1,857 1,858 1,854 1,935 1,959 2,051 1,938 2,272
Summer 1,930 1,922 1,909 2,001 2,040 2,117 2,012 2,372
42 Usquepaug River-Pawcatuck River 010900050204 100 Winter 4,474 4,382 4,373 4,479 4,601 4,821 4,691 4,848
Summer 4,705 4,740 4,728 4,844 5,109 5,237 4,941 5,131
43 Tomaquag Brook-Pawcatuck River 010900050205 100 Winter 6,404 6,554 6,611 6,559 6,657 6,318 6,773 6,785
Summer 6,641 6,898 7,040 7,100 7,211 6,991 7,401 7,401
44 Ashaway River 010900050301 17 Winter 916 903 889 956 974 995 960 1,041
Summer 936 925 933 993 994 1,044 1,040 1,106
45 Outlet Pawcatuck River 010900050303 52 Winter 18 16 16 15 15 13 16 10
Summer 18 16 16 15 15 13 16 10
46 Saugatucket River 010900050401 100 Winter 257 263 264 275 261 261 253 289
Summer 259 263 265 278 263 264 257 293
47 Point Judith Pond-Frontal Block Island Sound 010900050402 100 Winter 169 172 166 160 150 150 156 150
Summer 288 295 297 303 288 304 274 276
48 Ninigret Pond-Frontal Block Island Sound 010900050403 99 Winter 3,845 3,769 3,819 3,776 3,727 3,682 4,147 3,938
Summer 6,425 6,593 6,546 6,330 6,360 6,322 7,083 6,789
49 Block Island 010900050404 97 Winter 531 536 525 494 483 535 851 601
Summer 2,329 2,302 2,168 2,187 2,216 2,305 7,016 2,454
50 Upper Fivemile River 011000010301 30 Winter 665 671 680 686 800 757 682 796
Summer 715 725 751 764 851 883 774 884
51 Lower Fivemile River 011000010302 20 Winter 333 333 329 335 391 383 333 408
Summer 350 349 356 366 409 420 367 441
52 Upper Moosup River 011000010501 97 Winter 2,654 2,623 2,658 2,745 2,474 2,574 2,659 2,678
Summer 2,673 2,646 2,676 2,764 2,505 2,587 2,682 2,706
53 Quaduck Brook 011000010502 32 Winter 621 549 555 585 514 557 531 615
Summer 626 554 559 590 519 557 531 615
54 Upper Pachaug River 011000010601 4 Winter 9 10 9 7 7 6 7 5
Summer 9 10 9 8 8 7 9 5
Rhode Island Summer 117,044 117,409 116,925 117,057 117,337 117,625 125,323 122,059
Winter 108,192 107,985 107,781 107,729 107,419 107,435 109,658 110,745
Table 2.    Populations who use domestic self-supply wells in Rhode Island by 12-digit hydrologic unit code (HUC12) subwatershed for calendar years 2014–2021.

Water Use and Water Withdrawal

The median daily per capita domestic water use rate calculated in this study from the 19 PWSs was 46.0 gpcd, and the 95-percent confidence interval was 20.1–108.2 gpcd (fig. 9). Overall, seasonality was significant (Kruskal-Wallis test on months, p < 0.05): the highest daily per capita domestic water use rates were in August–October (medians of 56.3, 55.5, and 54.4 gpcd, respectively), and the lowest daily per capita domestic water use rates were in March–May (medians of 39.1, 39.3, and 38.5 gpcd, respectively). No significant annual trend was seen over the period of this study in the daily per capita domestic water use rates (seasonal Mann-Kendall test, 11 degrees of freedom, p = 0.29).

Graph showing daily per capita domestic water use coefficients by month in Rhode Island
                           for 2014–21. Rates from Chamberlin and Armstrong (2024).
Figure 9.

Graph showing daily per capita domestic water use coefficients by month in Rhode Island for 2014–21. Rates from Chamberlin and Armstrong (2024).

The greatest amount of domestic self-supply water withdrawal occurred in the western part of the State, which is the area with the largest number of people who rely on self-supply wells (fig. 10). Total self-supplied domestic withdrawals varied by municipality and drainage basin, and the greatest total annual withdrawals were in the towns of Scituate (an average of 0.459 Mgal/d between July 2014 and June 2021) and Charlestown (an average of 0.438 Mgal/d between July 2014 and June 2021), and in the drainage basins of the Tomaquag Brook-Pawcatuck River2 (an average of 0.379 Mgal/d between 2014 and 2021) and Woonasquatucket River3 (an average of 0.342 Mgal/d between 2014 and 2021; tables 3 and 4). Statewide, total monthly withdrawals from private wells ranged from 3.987 Mgal/d in March 2018 to 7.767 Mgal/d in September 2016, and no trend over time was detected in the monthly values (seasonal Mann-Kendall test on months, 11 degrees of freedom, p = 0.24; fig. 11). Statewide, water withdrawals from self-supply wells are generally higher in summer than in winter, similar to the seasonal pattern of use for PWSs (Stagnitta and Medalie, 2023).

3

HUC12 010900040502.

2

HUC12 010900050205.

Values range from 0 gallons per day to 0.38 million gallons per day. The subwatersheds
                        with the largest withdrawals are labelled 12 and 43.
Figure 10.

Map of domestic self-supply water withdrawals in Rhode Island for fiscal year 2020 (July 2019–June 2020) for 12-digit hydrologic unit code (HUC12) subwatersheds. Data from Chamberlin and Armstrong (2024).

Seasonal patterns are strong and range from 1.5 to2 million gallons per day of difference
                        between summer and winter months.
Figure 11.

Graph showing time series of total domestic water withdrawals from self-supply wells in Rhode Island for 2014–21. Data from Chamberlin and Armstrong (2024).

Table 3.    

Annual domestic self-supply water withdrawals by municipality in Rhode Island for fiscal years 2015–21 (July 2014–June 2021).

[Data from Chamberlin and Armstrong (2024). Fiscal year is defined as the 12-month period from July 1 to June 30 and designated by the calendar year in which it ends. Mgal/d, million gallons per day]

Table 3.    Annual domestic self-supply water withdrawals by municipality in Rhode Island for fiscal years 2015–21 (July 2014–June 2021).
Barrington 0.004 0.003 0.003 0.003 0.003 0.003 0.004
Bristol 0.084 0.088 0.093 0.094 0.097 0.087 0.081
Burrillville 0.312 0.308 0.262 0.259 0.285 0.316 0.341
Central Falls 0 0 0 0 0 0 0
Charlestown 0.466 0.461 0.47 0.442 0.416 0.457 0.357
Coventry 0.424 0.432 0.386 0.365 0.38 0.37 0.437
Cranston 0.068 0.068 0.068 0.06 0.06 0.061 0.069
Cumberland 0.06 0.059 0.057 0.054 0.05 0.055 0.055
East Greenwich 0.051 0.053 0.051 0.049 0.052 0.047 0.053
East Providence 0.002 0.002 0.002 0.002 0.002 0.002 0.002
Exeter 0.347 0.338 0.315 0.321 0.295 0.285 0.309
Foster 0.197 0.193 0.2 0.205 0.168 0.183 0.202
Glocester 0.387 0.388 0.366 0.352 0.369 0.394 0.423
Hopkinton 0.466 0.44 0.425 0.414 0.364 0.395 0.375
Jamestown 0.139 0.132 0.137 0.13 0.133 0.127 0.148
Johnston 0.09 0.093 0.089 0.078 0.08 0.076 0.081
Lincoln 0.004 0.004 0.004 0.003 0.003 0.004 0.004
Little Compton 0.203 0.197 0.2 0.196 0.2 0.205 0.236
Middletown 0.093 0.081 0.079 0.07 0.067 0.065 0.071
Narragansett 0.003 0.003 0.003 0.003 0.003 0.003 0.002
New Shoreham 0.051 0.035 0.035 0.04 0.035 0.037 0.054
Newport 0.004 0.003 0.004 0.004 0.004 0.006 0.008
North Kingstown 0.059 0.059 0.057 0.056 0.056 0.059 0.067
North Providence 0 0 0 0 0 0 0
North Smithfield 0.317 0.319 0.301 0.316 0.333 0.344 0.372
Pawtucket 0 0 0 0 0 0 0
Portsmouth 0.024 0.022 0.023 0.022 0.022 0.025 0.032
Providence 0 0 0 0 0 0 0
Richmond 0.358 0.342 0.318 0.326 0.292 0.301 0.326
Scituate 0.467 0.463 0.485 0.458 0.443 0.435 0.465
Smithfield 0.177 0.174 0.182 0.167 0.172 0.167 0.179
South Kingstown 0.145 0.148 0.15 0.152 0.153 0.17 0.178
Tiverton 0.218 0.165 0.207 0.244 0.246 0.323 0.353
Warren 0.021 0.022 0.018 0.019 0.018 0.019 0.021
Warwick 0.004 0.004 0.004 0.004 0.004 0.003 0.004
West Greenwich 0.261 0.263 0.243 0.23 0.225 0.214 0.247
West Warwick 0 0 0 0 0 0 0
Westerly 0.035 0.033 0.038 0.035 0.031 0.035 0.045
Woonsocket 0 0 0 0 0 0 0
Rhode Island 5.54 5.4 5.28 5.18 5.06 5.27 5.6
Table 3.    Annual domestic self-supply water withdrawals by municipality in Rhode Island for fiscal years 2015–21 (July 2014–June 2021).

Table 4.    

Annual domestic self-supply water withdrawals by 12-digit hydrologic unit code (HUC12) subwatershed in Rhode Island for fiscal years 2015–21 (July 2014–June 2021).

[Data from Chamberlin and Armstrong (2024). HUC12s from U.S. Geological Survey (2020), accessed with nhdplusTools (Blodgett and Johnson, 2023). Map labels correspond to labels on figure 10. Fiscal year is defined as the 12-month period from July 1 to June 30 and designated by the calendar year in which it ends. Mgal/d, million gallons per day; —, no data]

Table 4.    Annual domestic self-supply water withdrawals by 12-digit hydrologic unit code (HUC12) subwatershed in Rhode Island for fiscal years 2015–21 (July 2014–June 2021).
1 Westport River 010900020502 12 0.076 0.047 0.07 0.088 0.086 0.123 0.133
2 Cold Brook-Rhode Island Sound 010900020503 77 0.142 0.136 0.14 0.137 0.141 0.143 0.164
3 Clear River 010900030202 75 0.172 0.17 0.146 0.144 0.153 0.166 0.188
4 Chepachet River 010900030203 100 0.162 0.162 0.143 0.136 0.142 0.163 0.17
5 Branch River 010900030204 98 0.269 0.268 0.23 0.231 0.254 0.285 0.311
6 Mill River 010900030205 2 0 0 0 0 0 0 0
7 Emerson Brook-Blackstone River 010900030206 28 0.095 0.099 0.096 0.101 0.108 0.108 0.109
8 Abbott Run 010900030207 58 0.036 0.035 0.033 0.032 0.031 0.033 0.033
9 Peters River-Blackstone River 010900030208 75 0.066 0.066 0.064 0.063 0.061 0.065 0.069
10 Ten Mile River 010900040401 12 0 0 0 0 0 0 0
11 Moshassuck River 010900040501 100 0.006 0.007 0.007 0.006 0.007 0.008 0.01
12 Woonasquatucket River 010900040502 100 0.343 0.342 0.352 0.334 0.343 0.33 0.353
13 Big River 010900040601 100 0.129 0.13 0.12 0.116 0.112 0.111 0.132
14 Flat River Reservoir 010900040602 100 0.308 0.317 0.286 0.274 0.288 0.28 0.327
15 South Branch Pawtuxet River 010900040603 100 0 0 0 0 0 0 0
16 Moswansicut Pond-Huntinghouse Brook 010900040604 100 0.286 0.277 0.288 0.273 0.257 0.246 0.26
17 Barden Reservoir-Ponaganset River 010900040605 100 0.143 0.134 0.137 0.139 0.113 0.134 0.145
18 Scituate Reservoir 010900040606 100 0.227 0.233 0.241 0.226 0.226 0.221 0.233
19 North Branch Pawtuxet River 010900040607 100 0.084 0.085 0.082 0.079 0.088 0.089 0.101
20 Pocasset River 010900040608 100 0.012 0.013 0.013 0.011 0.011 0.011 0.011
21 Pawtuxet River 010900040609 100 0.049 0.049 0.049 0.044 0.043 0.043 0.048
22 Palmer River 010900040701 6 0.004 0.003 0.003 0.002 0.002 0.002 0.003
23 Barrington River-Warren River 010900040702 51 0.003 0.003 0.003 0.003 0.003 0.003 0.004
24 Quequechan River 010900040803 20 0.073 0.059 0.066 0.071 0.071 0.102 0.119
25 Seekonk River-Providence River 010900040901 81 0.003 0.003 0.003 0.003 0.002 0.002 0.003
26 Old Mill Creek-Narragansett Bay 010900040902 40 0.004 0.004 0.004 0.004 0.003 0.004 0.004
27 Greenwich Bay 010900040903 85 0.003 0.003 0.003 0.002 0.002 0.002 0.003
28 Hunt River 010900040904 100 0.07 0.072 0.069 0.067 0.069 0.064 0.074
29 Mount Hope Bay 010900040905 21 0.097 0.102 0.103 0.106 0.109 0.098 0.095
30 Upper West Passage 010900040906 30 0.003 0.003 0.002 0.002 0.002 0.002 0.003
31 Upper East Passage 010900040907 53 0.016 0.015 0.016 0.015 0.015 0.018 0.025
32 Lower West Passage 010900040908 61 0.104 0.105 0.114 0.113 0.116 0.107 0.112
33 Lower East Passage 010900040909 36 0.084 0.068 0.063 0.054 0.052 0.055 0.073
34 Sakonnet River 010900040910 66 0.192 0.178 0.189 0.196 0.2 0.21 0.229
35 Aquidneck Island-Frontal Atlantic Ocean 010900040911 99 0.001 0.001 0.001 0.001 0.001 0.001 0.002
36 Pettaquamscutt River-Frontal Atlantic Ocean 010900040912 99 0.028 0.027 0.027 0.027 0.027 0.03 0.033
37 Upper Wood River 010900050101 86 0.353 0.341 0.298 0.287 0.259 0.251 0.275
38 Lower Wood River 010900050102 95 0.201 0.196 0.182 0.185 0.164 0.165 0.169
39 Chipuxet River-Pawcatuck River 010900050201 100 0.062 0.063 0.064 0.063 0.063 0.069 0.069
40 Usquepaug River 010900050202 100 0.264 0.258 0.246 0.258 0.241 0.227 0.259
41 Beaver River 010900050203 100 0.11 0.104 0.097 0.103 0.091 0.09 0.102
42 Usquepaug River-Pawcatuck River 010900050204 100 0.225 0.221 0.219 0.221 0.225 0.24 0.235
43 Tomaquag Brook-Pawcatuck River 010900050205 100 0.405 0.391 0.404 0.382 0.341 0.38 0.347
44 Ashaway River 010900050301 17 0.059 0.054 0.056 0.055 0.049 0.056 0.051
45 Outlet Pawcatuck River 010900050303 52 0.001 0.001 0.001 0.001 0.001 0.001 0.001
46 Saugatucket River 010900050401 100 0.013 0.013 0.013 0.013 0.012 0.013 0.013
47 Point Judith Pond-Frontal Block Island Sound 010900050402 100 0.011 0.011 0.011 0.01 0.01 0.011 0.011
48 Ninigret Pond-Frontal Block Island Sound 010900050403 99 0.283 0.28 0.283 0.259 0.244 0.277 0.212
49 Block Island 010900050404 97 0.051 0.035 0.035 0.04 0.035 0.037 0.054
50 Upper Fivemile River 011000010301 30 0.026 0.027 0.023 0.025 0.028 0.029 0.032
51 Lower Fivemile River 011000010302 20 0.013 0.012 0.011 0.011 0.012 0.014 0.016
52 Upper Moosup River 011000010501 97 0.146 0.15 0.144 0.137 0.13 0.13 0.152
53 Quaduck Brook 011000010502 32 0.025 0.022 0.024 0.026 0.019 0.022 0.025
54 Upper Pachaug River 011000010601 4 0.001 0.001 0 0 0 0 0
Rhode Island 5.54 5.4 5.28 5.18 5.06 5.27 5.6
Table 4.    Annual domestic self-supply water withdrawals by 12-digit hydrologic unit code (HUC12) subwatershed in Rhode Island for fiscal years 2015–21 (July 2014–June 2021).

Discussion

The estimates of domestic self-supply water withdrawals from private wells are largest in rural, less populated parts of the State. Self-supply withdrawals are generally highest in summer, when water use per capita is highest (largely due to increased water use for outdoor purposes, such as irrigating lawns, maintaining swimming pools, and watering gardens) and when populations increase in areas popular for summer tourism. Self-supply withdrawals appear to be largely consistent over the period of this study (July 2014–June 2021), though the population of Rhode Island increased over this time, especially after 2019. Statewide, domestic self-supply water withdrawal is a small fraction of the State’s water budget: summer peak withdrawals were <8 Mgal/d, as compared with an estimated 120 Mgal/d for summer averages from all reported and estimated public-supply withdrawals (Rhode Island Water Resources Board, 2022). Locally, however, domestic self-supply wells may be the largest source of water withdrawal within a municipality or subwatershed (HUC12), and providing this previously unavailable information can assist with planning in these areas. Additionally, periods of high withdrawal frequently correspond to periods of low groundwater levels during hot and dry summers.

Our estimates of the domestic self-supply population are compatible with estimates for Rhode Island from other national and regional studies. Using two methods to estimate housing units using domestic self-supply wells in 2010, Murray and others (2021) produced estimates of roughly 10,000 housing units (based on the number of reported wells) and 60,000 housing units (based on the net housing units). With an average of 2.43 people per household for 2018–22 (Manson and others, 2023), 10,000 to 60,000 housing units is equivalent to 24,300–145,800 people who use domestic self-supply wells. Johnson and others (2019) estimated the population who use self-supply wells in Rhode Island to be 100,001 to 250,000 people in 2010. This study estimated 107,419–125,323 people served by domestic self-supply wells in the State between 2014 and 2021. The wide ranges of estimates in Murray and others (2021) and Johnson and others (2019) demonstrate the difficulty of precisely estimating domestic self-supply and why smaller scale studies, such as this one, can be useful in generating more precise local estimates. At the drainage basin scale, the results of this study were similar to estimates from a 1995–99 study (Wild and Nimiroski, 2007). In drainage basins that overlap between the two studies, we estimated an average of 23,890 people who use self-supply wells in the Pawtuxet River drainage basin4 (compared with 26,784 people in Wild and Nimiroski [2007]) and 4,360 people in the Quinebaug River drainage basin5 (compared with 4,501 people; Quinebaug River not shown on any map). The decrease in the population who use self-supply wells from 1995–99 to the period described in this study is consistent with the negative population change coefficients seen between 2014 and 2021 for many census block groups in the interior western parts of the State (fig. 5).

5

HUC12s 011000010301, 011000010302, 011000010501, 011000010502, and 011000010601.

4

HUC12s 010900040601, 010900040602, 010900040603, 010900040604, 010900040605, 010900040606, 010900040607, 010900040608, and 010900040609.

Wild and Nimiroski (2007) also estimated water withdrawal from domestic self-supply wells in the Pawtuxet River and Quinebaug River drainage basins. Though different methods were used to estimate withdrawal in this study, our results are largely consistent with their estimates from the 1990s and overall trends. Wild and Nimiroski (2007) constructed detailed water budgets of the Pawtuxet River drainage basin and Rhode Island portions of the Quinebaug River drainage basin and estimated annual domestic self-supply withdrawals of 1.915 Mgal/d for the Pawtuxet River drainage basin and 0.319 Mgal/d for the Quinebaug River drainage basin. Over the time period of this study (20 years after the study period of Wild and Nimiroski [2007]), we estimated average annual domestic self-supply withdrawals of 1.198 Mgal/d for the Pawtuxet River drainage basin and 0.205 Mgal/d for the Quinebaug River drainage basin. The decreases in water withdrawals are consistent with a decrease in population in the drainage basins and also decreases of the per capita water use coefficients. Nationally, domestic water use has been declining because of many factors, including technological advancements and government policies (DeOreo and Mayer, 2012; Dieter and others, 2018). Wild and Nimiroski (2007) used per capita water use coefficients of 71 gallons per person per day, whereas the calculated per capita water use coefficients in this study were typically less than this value (fig. 9).

Conclusions

Understanding the spatial and temporal distribution of water withdrawals from private domestic wells is necessary for a complete accounting of domestic water withdrawals throughout Rhode Island. This understanding is also important because of the greater potential for drinking water contamination in private wells as a result of increased vulnerabilities and lower testing requirements (DeSimone and others 2014). Water withdrawal through private wells in Rhode Island occurs primarily in the western parts of the State. The spatial patterns closely correspond to the estimates of population density in areas not served by public water supply.

The U.S. Geological Survey, in cooperation with the Rhode Island Water Resources Board, found that water withdrawals through private wells account for a small portion of the State’s total domestic water withdrawals and that, statewide, annual withdrawals have been steady between 2014 and 2021. Though populations who use domestic self-supply wells have increased in Rhode Island between 2014 and 2021, and though substantial seasonal fluctuation in the domestic self-supply population exists, there have been no statistically significant annual or seasonal trends in domestic self-supply water withdrawals between 2014 and 2021. Withdrawals from private wells are largest in the inland areas of the western part of the State, and the towns of Scituate and Charlestown have the highest estimated withdrawals. Statewide withdrawals ranged from 3.987 to 7.767 million gallons per day over the study period. The median per capita domestic water use rate was 46.0 gallons per capita per day. With the estimates from this study, water-budget and availability of individual basins can be studied in more detail.

This study produced newly available monthly and annual 30-meter dasymetric rasters of estimates of populations who rely on domestic self-supply wells and water withdrawal from these wells for the state of Rhode Island. These products complement the withdrawal and population information currently available for domestic water use for public water systems. The combination of these products may assist water managers and planners in providing estimates of total withdrawal for domestic use at any spatial resolution, including subwatersheds, municipality boundaries, or counties. As water demands from future development projects are considered, a unified and complete estimate of current and historical water withdrawals for domestic use can be useful for managing Rhode Island’s water resources.

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Conversion Factors

U.S. customary units to International System of Units

Multiply By To obtain
foot (ft) 0.3048 meter (m)
yard (yd) 0.9144 meter (m)
acre 0.004047 square kilometer (km2)
gallon (gal) 3.785 liter (L)
gallon (gal) 0.003785 cubic meter (m3)
million gallons (Mgal) 3,785 cubic meter (m3)
gallon per day (gal/d) 0.003785 cubic meter per day (m3/d)
million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3/s)

Datums

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Abbreviations

ACS1

U.S. Census Bureau American Community Survey 1-year

ACS5

U.S. Census Bureau American Community Survey 5-year

gpcd

gallons per capita per day

HUC12

12-digit hydrologic unit code

PWS

public water system

RIWRB

Rhode Island Water Resources Board

SDWIS

Rhode Island Safe Drinking Water Information System

WUNDR

Rhode Island Water Use Needs, Data, and Reporting database

For more information about this report, contact:

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U.S. Geological Survey

10 Bearfoot Road

Northborough, MA 01532

dc_nweng@usgs.gov

or visit our website at

https://www.usgs.gov/centers/new-england-water

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Suggested Citation

Chamberlin, C.A., Armstrong, I.P., and Stagnitta, T.J., 2024, Estimating domestic self-supplied water use in Rhode Island, 2014–21: U.S. Geological Survey Scientific Investigations Report 2024–5109, 29 p., https://doi.org/10.3133/sir20245109.

ISSN: 2328-0328 (online)

Study Area

Publication type Report
Publication Subtype USGS Numbered Series
Title Estimating domestic self-supplied water use in Rhode Island, 2014–21
Series title Scientific Investigations Report
Series number 2024-5109
DOI 10.3133/sir20245109
Year Published 2024
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) New England Water Science Center
Description Report: vii, 29 p.; Data Release
Country United States
State Rhode Island
Online Only (Y/N) Y
Additional Online Files (Y/N) N
Google Analytic Metrics Metrics page
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