In the United States, the rate of consumption of drinking water is almost 100 gallons per person per day. Only a small portion of the "drinking water" supplied by public water systems is actually used for drinking; other uses include toilet flushing, bathing, cooking, cleaning, and lawn watering. Drinking-water supplies in large cities come from surface-water sources such as lakes, rivers, and reservoirs. In rural areas, groundwater is more likely to be the source of drinking water. In this case, groundwater is pumped from a well that taps into aquifers. Rain and snow precipitation are also collected and used for this purpose.
Groundwater, which is the main source of drinking water for almost half of the population of the United States, is normally free of suspended solids, bacteria, and other disease-causing organisms. Due to agricultural runoff or disposal of liquid waste, however, groundwater is being contaminated. Groundwater is relatively inexpensive and easy to access, but it is limited in volume and thus irreplaceable if depleted. To avoid such an occurrence, many states are creating ways for rainfall to move into holding ponds so that water can recharge aquifers by entering the ground again.
Another potential source of drinking water is runoff from rainfall, which can be used to supply large municipalities. This water is collected and treated before being distributed for human consumption.
Surface water requires extensive treatment before it can be distributed for human consumption. Sources of surface water include lakes, streams, and rivers.
The 1974 Safe Drinking Water Act was used by the Environmental Protection Agency (EPA) to set a series of primary standards to protect human health, as well as secondary standards that deal with the temperature, color, taste, and odor of drinking water. The primary standards consist of maximum contaminant levels (MCLs) for specific inorganic contaminants, volatile organic chemicals, and radioactive materials, as well as limits for turbidity and coliform organisms. The EPA also identified the following treatment processes as being effective in removing or reducing the levels of contaminants: conventional coagulation, sedimentation, and filtration; or lime softening treatment.
Societal concerns for the quality of water resources continue as many of the streams and coastal waters do not meet water-quality goals. States report that 40 percent of the waters surveyed are too contaminated for drinking, fishing, or swimming. Since the signing of the Clean Water Act in 1972, public and private sectors have spent more than $500 billion on water pollution control.
MARK G. ROBSON
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