The domestic water-use activities include withdrawals from ground and surface water; deliveries from public water suppliers; consumptive use in the form of evaporation, usually during outdoor use, but also through washing and cooking; releases into wastewater-collection systems; and return flow, usually through septic systems (fig. 4).
11.D.2. Sources of domestic water-use information
Important sources for most of the above recommended domestic water-use
data are (1) studies of domestic water use by any of several State
agencies, including those responsible for water-data collection, safe
drinking water, planning, or water-resource management; and (2) public
water suppliers and wastewater-treatment systems, including studies
done for them by consulting firms.
11.D.3. Measurement, estimation, and data-collection methods for
domestic water use
Domestic water withdrawals and return flow usually are determined by
multiplying the self-supplied or self-disposed population by a per
capita value (coefficient of water use per person per day).
Deliveries to domestic users are determined from public water-supply
customer records or from estimation methods described in the public
water-supply section of this chapter. Releases after domestic use are
determined from wastewater treatment customer records or estimation
methods described in the wastewater collection and return flow section
of this chapter. Evaporation consumptive use is estimated.
Figure 4. Diagram of domestic water use.
Statistical sampling techniques can be applied to select a population from which measurement of domestic use can be made. The actual measurements are done by reading existing meters or by measuring the pumping rate and using time totalizers to record pumping duration. Possible criteria for developing stratified subsets include the number of households in the unit or size of lot. Residents may be surveyed to determine other important criteria, such as family size, age distribution, income, number of bathrooms, or participation in conservation programs. The coefficients tied to these criteria can be used with the U.S. Bureau of the Census data to estimate domestic use in similar areas.
The second locally derived per capita correlation method may be developed after a careful review of public water supply or wastewater-treatment customer records. Because some wastewater-treatment facilities charge fees according to metered use, self-supplied housing units that release water to the facilities may be metered for billing purposes. However, careful examination of these records could take as long as doing meter readings of selected households if the records are not automated with sufficient data to determine the actual use. In addition, population-served data may be difficult to obtain and correlate.
The third method involves using per capita use estimates from other organizations or published reports. Many studies have been done throughout the country documenting domestic water use, (see reference list in this section). The U.S. Department of Housing and Urban Development conducted a nationwide study in 1984 to document how people use water in their homes. This study has been adapted to regional conditions in many parts of the country. Average annual domestic use in the Delaware River Basin use is calculated in (Featherstone, 1991) the following manner (table 2):
(1) PCU(a) = 3(PCU(o) + PCU(i)) + 6(1/2PCU(o) + PCU(i)) + 3PCU(i) 11
where PCU(a) is the average annual per capitause;
PCU(o) is the outdoor per capita use, and
PCU(i) is the indoor per capita use.
Table 2 is useful in adapting published per capita values to local conditions. Nationally, self-supplied per capita values range from 40 gal/d to 125 gal/d (Solley and others, 1993), with a mean value of 79 gal/d and a standard deviation of 21. Fifty percent of the values (the interquartile range) fall between 67 and 88. Generally, the higher per capita uses are in the West.
Regional planning agencies, State planning agencies, State resource agencies, or the State public health agencies or consulting firms are possible sources for per capita information. However, caution must be exercised in using per capita estimates derived by other studies. Differences in definitions and methods of calculating per capita water use may effect the comparability of estimates. For example, per capita values based on total withdrawals by public water suppliers will be higher than those per capita values based on deliveries to domestic customers.
The self-supplied population may be determined by subtracting the permanent resident population served by public water supply from the total population. The estimated self-supplied population will be too low if nonresidents are included in the population served. When using this technique, vacationers and users of second homes are not considered residents. Resident population estimates may be obtained from county planners or consulting firms who have recently studied developments of second homes in an area.
Table2. Breakdown of domestic consumptive use pre-1980 and post 1980 fixture implementation.
Consumptive use is estimated for self-supplied and delivered domestic water. Domestic consumptive use is typically estimated by a percentage of water that is withdrawn and delivered for domestic purposes. Percentage of consumptive use should be based on information obtained from contacts with water suppliers or from references for each state. The largest amount of domestic consumptive use probably is from lawn watering, because most lawn water is evaporated or transpired. Therefore, estimates of lawn watering are useful when estimating domestic consumptive use.
Lawn-watering records occasionally are maintained by operators of sewage-treatment facilities. The records are used to credit water users (who wish to buy a meter) for water not released to the treatment facilities. Amounts not released are subtracted from water users wastewater-treatment bills. In some cases, water used for lawn watering can be estimated from monthly data by calculating the difference between the amount of water used in the growing season and that used in the winter. This was the method used by Featherstone (1991) and is included in table 2. Equation (1) could be used to calculate consumptive use and would be changed in different sections of the country. In the temperate north, outdoor use peaks only for 3 months, and may be about half of the peak for the 6 spring and fall months, and 0 for the 3 winter months. In the warmer areas, peak summer use may be for 9 months, and half peak use for the 3 winter months. The value for summer outdoor use will also vary in different parts of the country. In the east, summer outdoor use is 28 gal/d in the New Jersey/Pennsylvania area. In the more arid west, summer use is considerably higher which is why western per capita values are generally higher than eastern ones.
In California, studies of statewide domestic water use (California Department of Water Resources, 1983, p. 9) indicate that about the same quantities of water are used inside and outside of dwellings. Usually more than half of the outside landscape irrigation water evaporates or is transpired by trees and plants. Conversely, only about 2 percent of the water used inside evaporates. The remainder of the inside water use is discharged to the sewer and becomes available for reuse. This information can be used to make a conservative estimate of domestic consumptive use of water.
Agthe, D.E., Billings, R.B., and Dworkin, J.M., 1988, Effects of rate structure knowledge on household water use: Water Resources Bulletin, v. 24, no. 3, p. 627-630.
Baumann, D.D., Boland, J.J., and Sims, J.H., 1981, The evaluation of water conservation for municipal and individual water supply, illustrative examples: Fort Belvoir, Va., U.S. Army Corps of Engineers, Institute for Water Resources, contract report 82-C1, 356 p.
Bruvold, W.H., and Smith, B.R., 1988, Developing and assessing a model of residential water conservation: Water Resources Bulletin, v. 24, no. 3, p. 661-669.
California Department of Water Resources, 1983, Urban water use in California: California Department of Water Resources Bulletin 166-3, 239 p.
Claborn, B.J., Trauth, K.M., West, R.L., Urban, L.V., 1988, Residential water use study of Lubbock, Texas, in Symposium on Water-Use Data for Water-Resources Management, Tucson, Ariz., 1988, Proceedings: American Water Resources Association, TPS-88-2, p. 872.
DiNatale, K.N., 1981, An assessment of water use and policies in northern Colorado cities: Fort Collins, Colorado Water Resources Research Institute, 200 p.
Featherstone, J.P., 1991, Economic and social benefits of low-consumption toilets in the Delaware River Basin: Annual Conference on Resources, Engineering and Operations for the New Decade, 1991, Proceeding:, in American Water Works Association, p 763-772.
Flack, J.E., 1981, Residential water conservation: American Society of Civil Engineers, Journal of the Water Resources Planning and Management Division, Proceedings Paper 16080, p. 85-95.
Goodrich, D.L., 1991, Analysis of a domestic water well survey: Water Well Journal, v. 45, no. 6, 32 p.
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Maddaus, W.O., 1987, The effectiveness of residential water conservation measures: Denver, Co., Journal of the American Water Works Association, March 1987.
McCray, K., 1986, Water well industry survey: Water Well Journal, v. 40, no. 9, 58 p.
Morgan, W.D., and Smolen, J.C., 1976, Climatic indicators in estimation of municipal water demand: Water Resources Bulletin, v. 12, no. 3, p. 511- 518.
Seaker, E.M., Sharpe, W.E., 1988, Water use in eight central Pennsylvania homes in Symposium on Water-Use Data for Water-Resources Management, Tucson, Ariz., 1988, Proceedings: American Water Resources Association, TPS-88-2, p. 872.
Seidel, H.F., 1985, Water utility operating data--an analysis: American Water Works Association Journal, v. 77, no. 5, p. 34-41.
U.S. Department of Commerce, 1982, 1980 Census of housing: U.S. Government Printing Office.
U.S. Department of Housing and Urban Development, 1984a, Residential water conservation projects--Summary report: Office of Policy, Development, and Research, Building Technology Division.
U.S. Department of Housing and Urban Development, 1984b, Survey of water fixture use: Office of Policy, Development, and Research, Building Technology Division.