Drinking Water Data

Safe and reliable drinking water keeps us healthy. In Washington State, 88 percent of us get our water from public water systems.

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• Drinking Water Data

Why is data about contaminants in drinking water important?

• If present in drinking water, nitrate can impair our blood's ability to transport oxygen. Nitrate contamination of drinking water can come from the agricultural use of fertilizers and manure, septic tank and wastewater effluent, and the disposal of animal wastes.
  • Less than 0.5 percent of our public water systems have reported nitrate levels above the federal limit of 10 mg/L.
• If present in drinking water, synthetic organic compounds (SOCs) such as Atrazine and Di [2-ethylhexyl] phthalate (DEPH), and volatile organic compounds (VOCs) such as tetrachloroethene, also called perchloroethylene (PCE), and trichloroethylenes (TCE) can cause a long-term potential health risk.
  • In Washington State these compounds rarely occur in our drinking water and all community water systems that were tested met the standard.
• Haloacetic acids (HAA5) are disinfection by-products (DBPs) formed when chlorine is used to disinfect water. HAA5 can vary seasonally and are generally tested every quarter on water systems where disinfection is necessary. If present in drinking water, DBPs can cause a long-term potential health risk.
  • About 0.8% of tested systems test above the maximum contaminant level of 60 µg/L.

Additional Resources

Drinking Water Program

Coliform Bacteria and Nitrates—Private Wells 331-171 (PDF)

Drinking Water Publications

Private Wells: Information for Owners 331-349 (PDF)

SENTRY Internet—Community Water System Information

Analysis of Contaminant Occurrence Data in Public Water Systems (Six Year Review)—EPA

National Report on Human Exposure to Environmental Chemicals—CDC

Radionuclides Rule for Drinking Water—EPA

Safe Drinking Water Act—EPA

Water—CDC