Public water supplies are utilized extensively by industries for processing, cooling, and steam generation. The requirements as to quality of water for each industry are specific, therefore information on the quality or chemical character of the water supply is essential not only in the location of industrial plants but also is an aid in the manufacture and distribution of products.

Data are given in this report on the water supplies for 1,315 of the larger cities (or places) throughout the United States. The population of these cities represents 58. 3 percent of the total population (1950 census), and more than 90 percent of the total urban population, of the United States. Part 1 of the report contains data for 819 cities east of the Mississippi River, and part 2 includes data for 416 cities west of the river. All cities of 15,000 or more population and many cities of smaller population are included.

The information given for each place includes, in most instances, population of the place; ownership, source, and treatment of supply; storage facilities for both raw and finished water; and chemical analyses of the supplies.

The chemical quality of a water affects its industrial utility. A total of 2, 506 chemical analyses of the supplies for the places included are shown. Surface-water supplies, generally, are more variable in composition than ground-water supplies, but contain less mineral matter in solution. Many of the treated public supplies require further treatment to make them satisfactory for some industrial uses. Of the total of 1,315 places included in the report, 711 receive surface-water supplies; 472 receive ground-water supplies, and 132 receive mixed supplies. The population served by these supplies is about 88,000,000, of which about 71,000,000 receive surface-water supplies and 17,000,000 groundwater supplies.

Hardness of water supplies with respect to industrial use is given much attention. The hardness of the large public supplies ranges from less than 5 parts per million to about 700 parts. About 52, 000, 000 people are furnished with water having hardness of 100 parts per million or less. The weighted average hardness (average hardness of supplies weighted according to the population served) of finished water of surface supplies is 82 parts per million; of ground supplies, 162 parts; and of all supplies, 97 parts.

The weighted average hardness of raw water of surface, ground, and all supplies are 96,200, and 116 parts per million, respectively. The average hardness (based on the average hardness of each supply and the number of supplies) of finished water of surface supplies is 85 parts per million; of ground supplies, 164 parts; and of all supplies, 121 parts.

The average hardness of the raw water supplies are 94, 192 and 139 parts per million, respectively.

The median hardness of finished water of all supplies is 91 parts per million, and of the raw water supplies, 90 parts.

The treatment of a public water supply is planned principally to give a water that is bacterially safe for public use, and to eliminate or minimize certain undesirable characteristics of the water; Of the supplies for the places in this report, a total of 117 (3 surface supplies and 114 ground supplies) receive no treatment; 393 supplies receive no treatment other than chlorination; and the remainder receive treatment in addition to chlorination. The supplies for 171 cities are softened. Rapid sand filter plants are in use for 533 cities, exclusive of those in use at places where the water is softened. Slow sand-filter plants are in use at 35 places. A population of about 40, 000, 000 is served with water from these filter plants.

The total number of treatment plants, exclusive of facilities for chlorination, for most of the places in this report is 660. The total capacity of these plants in millions of gallons per day is 10, 694. A total of 693 places report raw-water storage facilities having a total capacity of 2, 460, 346 millions of gallons; a total of 1,081 places report finished-water storage facilities having a total capacity of 24, 557 millions of gallons.

Investigations by others have shown that a definite relationship exists between fluoride in drinking water and the incidence of dental caries in the teeth of children. A total of about 85 percent of the population served from the large public supplies receive water having a fluoride concentration in the range of 0.0 to 0. 5 part per million. Few large public supplies contain fluoride in concentrations in excess of 3 parts per million. A total of 155 places of those included in the report received fluoridated water in 1955.