Water Sources

Rainwater falls on a watershed (catchment area) and either flows above ground to streams and rivers or soaks into the ground to reappear in springs or to be drawn from wells.

The amount of rainwater that will enter a water supply system depends on the amount of precipitation and the volume of precipitation and the volume of the runoff. About two thirds of the annual average precipitation in the United States is lost to the atmosphere by evaporation and transpiration. The remaining water becomes runoff into river and lakes or, though infiltration, replenishes ground water.

Surface water
Surface water is obtained from lakes, streams, rivers, or ponds. Storage reservoirs-artificial lakes created by constructing Dams across stream valleys-can hold back higher than average flows and release them when greater flows are needed. Water supplies may be taken directly from reservoir or from locations downstream of the dams.

Ground Water
Ground water supplies come from natural springs, from well, and from infiltration galleries, basins, or cribs. Most small, and many large, North American water systems use groundwater as their source of supply.

Water Reuse
Only a small portion of the water that is supplied to dwellings, commercial and industrial establishments, and public facilities is consumed by evaporation and processing. The remaining waste water (usually after treatment) is discharged to the soil and either infiltrates to groundwater or is discharged to surface water courses.