Drinking Water—Safety on Tap - Drinking Water Sources

The two primary sources of drinking water are fresh surface water and groundwater. In 2002 more than half (66%) of the population of the United States received water from sources that obtained that water from such surface water as lakes, rivers, and reservoirs. The remaining population (34%) was supplied with water that came from groundwater stored in aquifers. Aquifers are underground geologic formations that are made up of saturated layers of sand and rock fragments and store or transfer water. Aquifer water is obtained from wells and springs. In a few instances, desalinization is used to treat saltwater to make it fit to drink. Contaminants can enter water sources through a variety of pathways, but the level or amount of harmful substances in water is the main determinant as to whether the water can be treated and made safe to drink.