The public water supplies of the 100 largest cities in the United States (1960 U.S. Census) serve 9,650 million gallons of water per day (mgd) to 60 million people, which is 34 percent of the Nation's total population and 48 percent of the Nation's urban population. The amount of water used to satisfy the domestic needs as well as the needs of commerce and industry ranges from 13 mgd, which serves a population of 124,000, to 1,200 mgd, which serves a city of 8 million people.

The water for the public supplies of these largest cities comes fro^n ground water wells and infiltration galleries and from surface water streams, reservoirs, and lakes. Twenty of the cities use ground water exclusively for public supplies, and 14 use a combination of ground and surface waters. Sixty-six cities use surface water solely; of these cities 37 depend solely upon reservoir water, and 20 depend solely upon natural streamflow. Water from the Great Lakes furnishes part or all of the water supply for 10 of these largest cities.

Hardness of water, measured in parts per million (ppm), is an important factor in the usability of water supplies. Twenty-seven cities, serving a population of 8 million, have a raw-water hardness exceeding 180 ppm ("very hard"), but only 13 cities, serving a population of 3.7 million, have a "very hard" treated-water supply; and although 22 cities, serving about 10 million people, have a raw-water hardness ranging from 121 to 180 ppm ("hard"), only 16 cities, serving a population of 11 million, have a "hard" treated-water supply. Only 16 cities, serving a population of 16 million people, have a raw-water hardness ranging from 61 to 120 ppm ("moderately hard"), whereas 41 cities, serving a population of 22 million, have a treated-water supply having a hardness within this desirable range. A few cities that have a "soft" raw water add lime to control corrosion and consequently increase their water hardness to more than 61 ppm. Thirty cities, serving a population of about 23 million, have a treated-water supply with a hardness of less than 61 ppm.

The dissolved-solids content in raw-water supplies of 27 cities, which serve a total population of slightly more than 21 million people, is 100 ppr^ or less. Thirty-eight cities serving a total population of 23 million people have raw-water supplies with a dissolved-solids content between 101 and 250 ppm, whereas 48 cities, serving a population of 28 million about half the population of these 1 2 PUBLIC WATER SUPPLIES, 1962 cities furnish water having this range of dissolved solids. Twentv-nine cities serving a total population of 11 million people have raw-water supplies that contain between 251 to 500 ppm of dissolved solids. Because some o* these cities treat their water supply, 22 cities serving 8 million people furnish water having a dissolved-solids content between 251 and 500 ppm. Only six cities, serving a population of about iy2 million people, have raw-water supplies containing more than 500 ppm of dissolved solids; four of these cities soften the water and consequently reduce the dissolved-solids content. Thus, about 1 million people in three cities receive water containing more than 500 ppm of dissolved solids.

Chemical analyses of treated-water supplies indicate that more than 90 percent of the supplies contain less than (a) 500 ppm of dissolved solids, (b) 100 ppm of sulfate, (c) 50 ppm each of calcium, sodium, and chloride, (d) 30 ppm of silica, (e) 20 ppm of magnesium, (f) 5 ppm each of potassium and nitrate, and (g) 1 ppm of fluoride.

Spectrographic analyses, reported in micrograms per liter (/*g per 1), show that 87 percent of the treated-water supplies contain less than 500 /*g per 1 of aluminum and more than 90 percent of the supplies contain less than (a) 500 /*g per 1 of strontium, (b) 150 /*g per 1 of iron, (c) 50 ^g per 1 of lithium, (d) 10 /ug per 1 each of molybdenum, nickel, lead, and vanadium, and (e) 5 /*g per 1 each cf chromium, rubidium, and titanium.

Radiochemical analyses of treated-water supplies reveal that the maximum beta activity of these supplies is 130 picocuries per liter (pc per 1) and the maximum activity due to radium content is 2.5 pe per 1, both of which are well under the recommended maximum limits for drinking water.

The report is divided into two sections. The first describes the uses of water in large cities, the raw-water supplies available for public supplies, tl-<; major and minor constituents and the properties of water, the methods of analyses, the treatment of water, the effects of chemical treatment on constituents and properties of water, and the costs of water treatment. The second is a city-by-city inventory that gives (a) the population of the city, (b) the adjacent communities supplied by the city water system, (c) the total population served, (d) the sources of water supply (including auxiliary and emergency supplies), (e) the average amount of water used daily, (f) the lowest 30-day mean discharge of streams used for public supply during recent years, (g) the treatment of water, (h) the rated capacity of each water-treatment plant, and (i) the storage capacity for raw and finished water. For 58 of the cities, the sources of water, the location of water-treatment plants, and the areas served by the city system are shown on maps. Chemical, spectrographic, and radiochemical analyses of treated water and chemical and spectrographic analyses for many of the raw-water supplies are presented in tabular form.