Groundwater Wells
In addition to surface water sources in the Green River Watershed, Tacoma Water owns and operates 24 wells in and around Tacoma. These wells pump water from aquifers, which are underground layers of water, saturated sand and gravel.
Much of our groundwater comes from the South Tacoma wellfield, a key resource for our future drinking water supply. We began developing this wellfield in the early 1900s and today it includes 14 wells. They pump from productive aquifers that stretch from north of the Nalley Valley all the way to Lakewood.
The South Tacoma wells can produce up to 40 million gallons of water per day and are used during low river flows and in emergencies. Additional wells located throughout our service area can supply up to an additional 15 million more gallons per day.
Groundwater typically provides less than 5% of Tacoma’s total water supply in the summer and supplements water from the Green River at other times of the year. However, during drought conditions, groundwater can supply up to 50% of peak summer demand.
Our groundwater system plays a vital role in ensuring a reliable, resilient water supply for our community.
Protecting Our Groundwater Supply
We sample drinking water wells for bacteria and for traces of more than 150 different metals and chemicals. We also sample numerous dedicated monitoring wells. In addition, we sample our sources for PFAS (per- and polyfluoroalkyl substances) to ensure that our well water meets new federal standards. View more information about our plans for PFAS treatment.
Thousands of homes and hundreds of businesses are located above the aquifer that supplies the South Tacoma wellfield. Because of this, we work to educate area residents and businesses about ways to prevent drinking water contamination. We also have a partnership with several permitting agencies that, together, form a protective web for the well water that includes permits, monitoring, and inspections. We take our prevention and outreach efforts seriously to keep our water safe and reliable.