Water Treatment
How we care for your water
The Green River Filtration Facility in South King County is where we filter and disinfect the water we deliver to more than 300,000 people in our area.
Filtration keeps our water supply clean, safe and reliable. Here’s how the process improves the water:
- Removes harmful bacteria.
- Improves its taste and clarity.
- Reduces the amount of sediment and sand entering water pipes.
- Reduces byproducts from the disinfection process.
About the Green River Filtration Facility
Since 1913, Tacoma’s primary water supply comes from the Green River. Before we built the Green River Filtration Facility in 2015, the Green River was one of the few major unfiltered surface water supplies left in the U.S.
We built the filtration facility to mainly remove the harmful cryptosporidium bacteria from this water supply. Cryptosporidium can cause disease in humans. Though the Green River generally carries low levels of this bacteria, we needed to follow new national standards for water utilities and provide this treatment to protect public health. We do not currently have any issues with this organism.
What we use to treat your water
We treat your water with a few different chemicals before it reaches your home or business. This is a typical process in all local water utilities, and each step in the process helps protect your health and improve your water use experience.
Chemicals we use for water treatment
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Chlorine is the primary way we disinfect your water. While it does an excellent job of killing microorganisms that might be harmful to you, chlorine also reacts with natural organic material commonly found in surface water sources such as lakes, rivers and streams.
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Some water supplies contain fluoride, which is a natural mineral that helps fight tooth decay. Our water sources do not contain a significant amount of natural fluoride.
We currently put fluoride in the water supply because the public voted in favor of this practice in 1988 and 1989. That meant we started to add fluoride in 1994 to help improve dental health.
We base our fluoride amount on guidance from the federal Department of Health and Human Services (HHS) and the Washington State Department of Health (DOH) regulations. We recommend you ask your dentist about health benefits or concerns.
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We use ozone to fix any possible taste and odor issues. Using ozone on the water also means you get additional disinfection benefits, which makes our water even safer to drink. The chemical lasts only a few minutes after we add to the water. By the time the water leaves the treatment site and heads to you, the ozone is gone.
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We treat our Green River water supply with caustic soda (also known as sodium hydroxide) to help minimize the amount of lead and copper found in homes. Adding caustic soda to water raises its pH (a measurement of acidity), which helps make water less corrosive on plumbing. That reduces the amount of lead and copper that can dissolve into drinking water.