City of Mercer Island releases annual water quality report

The city’s annual water quality report has been released to Island residents.

Mercer Island’s drinking water is supplied by Seattle Public Utilities (SPU). The primary source for Islanders’ water is the Cedar River Watershed, and an alternate source is the south fork of the Tolt River. Snowmelt from the Cascade Mountains, along with rainfall, supplies SPU’s watersheds, providing drinking water for 1.4 million people in the greater Seattle area.

The Cedar treatment plant has been functioning for 10 years. Water is screened at the facility for the removal of debris such as leaves and twigs. Chlorine is added to disinfect the water of microbial contaminants, and fluoride is added to promote dental health. The water is also treated with lime for pH-adjusted corrosion control and to prevent lead from leaching in older plumbing systems, according to the report.

Water samples are collected on a daily basis. All federal standards are met or surpassed. SPU tests for the presence of radioactive, biological, inorganic, volatile organic and synthetic organic contaminants. Regulated substances include barium, cadmium, chlorine, fluoride, haloacetic acids [HAAs] - Stage 2, nitrate, TTHMs [Total Trihalomethanes] - Stage 2 and total organic carbon. Turbidity, or cloudiness, rated an average of 0.3 and the source was soil runoff. For copper and lead, five of 52 sample sites were located at Mercer Island residences. More lead than copper was detected — 3.6 and .096 percent, respectively — both from household plumbing corrosion and natural deposits erosion. The city recommends that residents minimize the risk of lead exposure by running tap water from 30 seconds to two minutes before drinking it or using it in cooking.

Regulations are set by the U.S. Environmental Protection Agency and the Washington State Department of Health.

The city purchased 730.4 million gallons of water from Seattle Public Utilities in 2012, and 57.7 million gallons have not been accounted for. A certain percentage of water is unaccounted for each year, and 4.8 percent marks a three-year annual average. The city’s attempts to reduce unaccounted-for water include replacing inaccurate water meters, inspecting and repairing fire hydrants, and conducting an annual systemwide leak detection survey. During the city’s annual water main distribution flushing program, city crews meter water usage. Water used during the city’s fire hydrant inspection and repair program is also metered. Residents are encouraged to report water leaks to the city, non-city vehicles connected to fire hydrants or non-metered hoses connected to hydrants.

The City of Mercer Island reminds residents never to pour fat, oil or grease down sinks. Doing so could cause costly problems within the sewer collection system. Such substances coat plumbing and underground piping and can become blockages when built up over time. Wastewater could then back up into streets, yards, parks and storm drains. Residents should also avoid flushing food scraps. Residents should always dispose of fat, oil and grease in a waste container and put it in the garbage. Dispose of food scraps with solid wastes, and put disposable diapers, creams, lotions, personal hygiene products and non-biodegradable wipes in the garbage.


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