Groundwater typically supplies about 10 percent of Tacoma's water in the summer and supplements the supply from the Green River at other times of the year. Tacoma Water samples its drinking water wells for bacteria and for traces of over 150 different metals and chemicals. Tacoma Water also samples numerous dedicated monitoring wells.

Homes for approximately 30,000 people, as well as hundreds of businesses, are located above the underground aquifer that supplies the wells in the South Tacoma wellfield. A great many of these businesses use, handle and store chemicals that can contaminate groundwater. In addition, most homes have numerous household chemicals, pesticides, and fertilizers that can contaminate groundwater if they are disposed of or applied improperly.

If a groundwater well is contaminated, we must either treat the water or replace the well so that enough water would continue to be available for customers. Both of these options are expensive. Preventing contamination is much less expensive and more effective than fixing a problem after it has occurred. We work hard to educate both residents and businesses who are located in areas above our drinking water aquifers about ways to prevent contamination of our drinking water.