Follow the Flow: Seattle's Drinking Water

Article Photo

By Morgan Greenseth

The water we drink literally becomes us: after all, more than 50 percent of our bodies are made of H20. But how often do we think about what we drink--where it comes from, what's in it and where it goes when we let it seep down the drain? Knowing what happens to our water before and after it arrives in our homes can help us further appreciate this essential part of life.

Just by being awake, we process (and lose) 2.5 quarts of water every day. Fortunately, the daily drinking water needs of Seattle's 1.3 million residents are available straight from the tap.

The water that pours out of our faucets can be traced all the way to the rain and snowpack of the Cascades, where water feeds into two protected watersheds located in the foothills near the city. Watersheds, or drainage basins, are areas of land where all the water from it drains to the same place. The Cedar River watershed (the water source that feeds Lake Washington and, by extension, Puget Sound) provides 70 percent of Seattle’s drinking water. Owned by the city of Seattle, the 90,000 acres of this watershed are fenced and locked to protect our valuable resource from contaminants. Our other water source is the South Fork Tolt River watershed that supplies 100 million gallons of drinking water per day. So which watershed does the water in your home come from? If you live north of Green Lake, you receive water from the Tolt River watershed, and if you live south of the lake your water comes from the Cedar River watershed.


The transformation of fresh water from the rivers into the drinking water in our glasses begins in these watersheds. The Cedar River watershed is actually one of six major drinking water systems in the country that doesn’t need to be filtered. Glaciers have left rock, gravel, sand and clay, also known as moraine, which naturally filters the water and adds minerals. The filtered water is retained in a transmission reservoir to allow for silt to settle out (think of a gigantic, natural version of a Brita).

Even naturally filtered water still needs to be retained in a reservoir and disinfected in a treatment facility. Both processes are completed at the watershed. After the retention time has passed, the water from the reservoir is pumped through different treatment stations. Water first passes through the ozone generation and injection facility, a process that disinfects, and also improves taste and odor. In the second station, a UV treatment (chosen in party because it minimizes the use of chemicals) disinfects against chlorine-resistant pathogens. Following this treatment, chlorine and lime are added to protect against corrosion and add another layer of disinfection. After this final step, the water is ready for distribution to our homes.

treatmentprocess.jpgThe Treatment Process

Even though drinking water (including bottled water) may still contain small traces of contaminants, choosing tap water is an easy, safe and environmentally conscious decision. Even the City of Seattle is saying no to bottles. Seattle city water is tested against 100 federal EPA standards, and measures up to equal or even better quality than bottled water. If you get a funny taste from your tap, the problem is likely your pipes, not the water itself. A tap filter provides an easy solution.

Any water that we don't consume flows down the drain into one of two destinations, a septic tank or a sewage treatment plant. The water in the septic tank evaporates or seeps into a waterwell while the sewage water must be treated. In both instances the water does get reused, however, it’s extremely wasteful to create drinkable water if we don’t even use it. Click here for some tips from King County on how to conserve water in your home.

cedarriverwatershed.jpg Cedar River Watershed

So, the next time you turn on the faucet, consider how fortunate we are in Seattle to have quality drinking water available directly from the taps in our homes. In order to maintain this convenient luxury, we need to stay mindful of where our water comes from and how to keep it clean and abundant.

Photo credits: Cedar Water Treatment Facility
Flickr, Creative Commons
Flickr, Creative Commons