Groundwater

Why it matters

Groundwater provides drinking water through wells and base flows for streams and rivers. Base flows are important for fish during dry summer months.

Various chemicals used or dumped on the ground’s surface can infiltrate into the ground, or leak from septic systems, and end up in groundwater. Once these pollutants enter underground waters, they can be difficult to detect and remove, polluting drinking and irrigation water. Because groundwater supplies many streams, especially in the late summer, pollutants in groundwater can end up in those rivers and streams.

What is groundwater?

Groundwater is water that collects or flows beneath the earth’s surface, percolating through and filling the porous spaces in soil, sediment, and porous rocks, as well as fractures in hard rock. Groundwater originates from rain, melting snow and ice, irrigation, surface water, and infiltrated stormwater. Groundwater fills aquifers so that wells can withdraw water, and emerges at the land surface as springs.

Over 60 percent of Washington residents get their drinking water from groundwater. Groundwater is also used for irrigation, agriculture, and industry.