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Public Water Supplies: Sources of Supply.—Underground waters are more feasible as sources in small communities, while large cities, with some exceptions, either go great distances for upland surface supplies or utilize the large lakes or rivers nearby. An inventory by the United States Public Health Service in 1948 showed that groundwater supplied almost 65 percent of the 16,747 United States communities served by water supplies; surface waters supplied 29.6 percent, and the remainder received both ground and surface supplies.
This is accomplished by water spreading on the surface from an adjacent stream at floodtime (a majority of projects are of this type), or by injecting water, usually from a public water supply system, into the wells. Water spreading is done on permeable flat lands adjoining the stream, either by plowing to provide ditches and furrows, or by excavating a series of basins from 1 to 10 acres in area. Replenishment of underground reservoirs from surface supplies has been practiced in the United States since 1889. A government survey estimated that 700 million gallons per day were recharged in 1955.
Much of what is called water chemistry is the chemistry of substances suspended or dissolved in water. Water analysis involves the determination of these substances and materials. Except for seawater and occasional brine wells, most surface and underground waters are relatively low in dissolved substances. The amounts of dissolved and suspended matter in water are generally measured in terms of parts per million parts of water, or ppm. What are known as mineral waters, which are popularly thought to have medicinal value, rarely ever have more than 5,000 ppm. dissolved matter. Most public water supplies do not exceed 300 ppm. Suspended matter, except for river water in flood stage, is rarely higher than 1,000 ppm., and is often quite low. |
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