Why is my water yellow?

Yellow water is caused by seasonally elevated levels of the natural occurring minerals iron and

manganese found in the Green River water supply. Discolored water is most often described as "yellow water", but can also appear slightly green, red, or brown. Customers most often notice yellow water against white backgrounds like bathtubs, sinks, toilets and hot tubs.

Is my water safe to drink?

Yes. Tacoma Water continues to meet all health-based drinking water standards. We effectively monitor, disinfect and routinely test for more than 150 different chemicals in our drinking water annually. We also test nearly 200 coliform bacteria samples from throughout our system monthly.

Existing standards for iron and manganese are considered "secondary" standards, which are based on aesthetics and not health-related concerns. The secondary standard for iron is 0.30 milligrams per liter and 0.05 milligrams per liter for manganese. Tacoma Water's levels for these minerals typically remain well below these standards. Sometimes in the later summer and early fall, however, we slightly exceed them. The Washington Department of Health confirms there is no known or suspected health risk to consumers from low levels of iron and manganese typically found in drinking water.

What seasonal conditions cause yellow water?

In the Eagle Gorge Reservoir behind Howard Hanson Dam, water nearest the surface warms during the summer and colder water sinks to the bottom. Eventually, the reservoir becomes separated into layers by temperature. As oxygen is used up in the deeper water, it cannot be easily replenished and depletes. Low oxygen levels can cause iron and manganese in the reservoir's sediments to dissolve into the water supply. When the iron and manganese react with chlorine and ozone at the water treatment plant, the minerals become even more visible in the water. Chlorine and ozone are required to help ensure the safety of the drinking water.

Has yellow water been a problem in the past?

Yes. Customers have reported yellow water in past years, but 2007 was the first year that our entire service area was affected. We believe that an increase in water storage in the Eagle Gorge Reservoir from the Additional Water Storage Project contributes to the higher levels of minerals.

Will I have yellow water next year?

Yes. For the near future, we will most likely see some degree of yellow water every year during late summer and early fall. Historically, customers begin to notice yellow water in late July with the color diminishing by early October.

Can Tacoma Water remove iron and manganese in water?

Not currently. Few effective treatment alternatives exist. The most common method is filtration; but we do not currently filter our supply. Chemicals intended to keep these minerals invisible are available, but are not likely feasible in our larger water system. Tacoma Water is actively evaluating the need for installing a filter plant in the future. The seasonal presence of yellow water is one of many factors being discussed.

What is Tacoma Water currently doing to improve yellow water?

Tacoma Water helps minimize yellow water by modifying operations where possible. We regularly collect and evaluate water quality information to better understand yellow water.

We also anticipate a decrease in yellow water when the U.S. Army Corps of Engineers completes improvements to Howard Hanson Dam, which will allow water to be drawn from upper levels in the reservoir, where iron and manganese concentrations are lower. Unfortunately, these improvements will not be complete for several years.

Who can I contact with additional questions?

For more information, please call Water Quality at (253) 502-8207.