Source water is untreated water taken from rivers, lakes or underground aquifers to supply private and public drinking water systems. There are two types of source water: surface water and groundwater.

Surface water is water that lays on the Earth’s surface such as lakes, rivers and streams. It is drawn into a drinking water system through an intake pipe. Surface water is easily contaminated by pollution flowing over the land or directly into lakes, rivers and streams. Pollution can also come from the air or from materials in the bottom of the stream or lake.

Groundwater is the water beneath the Earth’s surface found in the cracks and spaces between soil, sand and rock particles. It is drawn into a drinking water system through a well. Surface water and groundwater can be interconnected, with water flowing from one to the other. Groundwater can also be contaminated by pollutants that are deposited on the surface soil or underground but it often takes much longer for the contamination to reach a well than a surface water intake. For the same reasons it takes longer for contamination to reach a groundwater source it is also much more difficult to fix a groundwater contamination problem.