Press Release

California Water Service Tests For and Confirms No Mercury in Water Supply

Testing Conducted After Reports of Mercury in Russian River

GUERNEVILLE, Calif. — After news reports surfaced that elevated levels of mercury from the abandoned Mount Jackson Mercury Mine entered the Russian River, local water utility California Water Service (Cal Water) conducted special testing on the water serving its Guerneville customers. Testing confirmed that there were no detectable levels of mercury in the water supply.

Water provided to Cal Water's Guerneville customers in its Armstrong Woods system comes from two groundwater wells. Some Cal Water customers had become concerned about their water supply, however, after hearing news reports of mercury in the river water, according to Cal Water Local Manager Darin McCosker. Cal Water tests for mercury in accordance with the State Water Resources Control Board's Division of Drinking Water (DDW) requirements, but the utility took additional water samples to ensure that the water continued to meet all water quality standards.

 "Some water quality tests, including mercury, are conducted less frequently because their levels do not change as much over time," McCosker said. "But, protecting our customers' health and safety is our highest priority, and we will go above and beyond what's required to ensure their water always meets or surpasses all federal and state standards. That's part of our commitment to provide our customers and communities with quality, service, and value."

Water quality testing for mercury is required by DDW every three years. The maximum contaminant level for the constituent is 2 parts per billion. Since Cal Water began operating this system in 2000, all water quality test results for mercury have been "non-detect."

Cal Water serves approximately 1,900 service connections in the Redwood Valley area and about 2 million people through 480,300 service connections in California. The company, which has provided water service in the area since 2000, was ranked "Highest in Customer Satisfaction among Water Utilities in the West" in 2016 by J.D. Power in its inaugural Water Utility Residential Customer Satisfaction Study. Additional information may be obtained online at