Tacoma Water provides direct service to more than 300,000 people in the City of Tacoma, Pierce and King counties, and several other municipal water suppliers. The primary water supply for these municipalities is the unfiltered Green River, which began supplying Tacoma its water in 1913. The Green River had been one of the few remaining major unfiltered surface water supplies in the U.S. However, due to worries of bacteria infection outbreaks in similar environments, regulations strengthened and required water to be treated against the specific bacteria, cryptosporidium.
In December 2014, a new facility was opened to begin filtering the water supply to meet new national standards for public health protection. This new facility required ways to filter out the bacteria entirely from the water, and adding even more of a challenge, the facility would still need to operate during construction.