City of Mercer Island

To ensure tap water safety, the EPA and Washington Department of Health establish regulations limiting contaminant levels in public water systems. Similarly, FDA and Washington Agriculture Department set standards for bottled water to provide equivalent public health protection.

All water sources—whether tap or bottled—can reasonably contain small amounts of certain contaminants. Their presence doesn't necessarily indicate a health risk. Water sources include rivers, lakes, streams, ponds, reservoirs, springs, and wells. As water moves across land or underground, it dissolves naturally-occurring minerals, sometimes radioactive materials, and substances from animal or human activities.

Potential contaminants in source water include:

• Microbial Contaminants: Viruses and bacteria from sewage treatment facilities, septic systems, agricultural operations, or wildlife
• Inorganic Contaminants: Salts and metals occurring naturally or resulting from urban runoff, wastewater discharge, oil/gas production, mining, or farming
• Pesticides and Herbicides: From various sources including agriculture, urban stormwater runoff, and residential usage
• Organic Chemical Contaminants: Synthetic and volatile organic compounds, byproducts of industrial processes and petroleum production, also from gas stations, urban runoff, and septic systems
• Radioactive Contaminants: Either naturally occurring or resulting from oil/gas production and mining

For additional information about contaminants and potential health effects, contact the EPA's Safe Drinking Water Hotline at (800) 426-4791.

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