Late summer 2007, many Tacoma Water customers began reporting yellow water, which became most noticeable against a white background, like a sink, bathtub or toilet. In past years, this phenomenon had been observed in isolated areas, but in 2007 its impacts were unprecedented. We began conducting extensive testing of its Green River water supply to determine cause.

Yellow Water

Tests show an increase in levels of the minerals manganese and iron dissolved in the Green River water supply. Treatment of these contaminants with chemicals like chlorine and ozone cause these minerals to become visible by giving them a yellow tint. Drinking water rules label these minerals as “secondary” or aesthetic contaminants that can cause objectionable appearance or taste. They do not have any known health effects at the levels Tacoma Water found.

We also reviewed changes in the environment. We found that the additional storage increase in the watershed, combined with watershed flooding in November 2006, might have caused an increase in the mineral levels found in 2007.

We continue working to minimize impacts of the yellow water, but expect conditions in the Green River to remain similar in 2008.

The Army Corps of Engineers also continues making modifications to the process it uses to allow water to exit the dam, which could eventually lower levels of minerals dissolved in the river. These projects will not be complete for several more years.