Where does our water supply come from?

Drinking water comes from surface water or ground water. The water that comes from sources open to the atmosphere (such as rivers, lakes, and reservoirs) is called surface water. The water that comes from wells drilled into underground aquifers (geologic formations containing water) is called ground water. Generally, surface water systems require more treatment because of their exposure to the atmosphere and runoff from rain and snow.
 
Source(s):
United States Environmental Protection Agency (EPA) “Water on Tap: What You Need to Know”