Testing Your Water

Information for Private Well Owners

Contaminated Wells

Contaminants could show up in your drinking water, potentially putting your family's health at risk. Because you may not taste, smell, or see many types of contaminants, the state Department of Health (DOH) believes regular water testing is very important.

Well Water Testing

If you own a private well, you are responsible for testing your own water. In most counties when you buy or sell a home with a private well, the county health or planning department, or the lending institution involved, may require the seller to provide water-sampling results to show the water is safe to drink. Contact your local county health or planning department for information on the requirements and the testing needed.

DOH recommends that private well owners test their drinking water every year for coliform bacteria and nitrate. These two contaminants rapidly could affect a person's health—possibly even with just one drink of water. If your nitrate level is 5 milligrams per liter (mg/L) or higher, you may want to re-test in six months.

At least twice, while you own the well, we also suggest testing for arsenic – once in summer and again in winter – to check any seasonal influences that may occur. Though arsenic does not cause rapid health effects, continued consumption over a relatively short time could lead to health concerns. Many certified labs in Washington perform these tests. The 2010 costs generally range from $25 to $50 per test. Lab staff can answer questions and tell you how to collect water samples. Private Wells: Information for Owners 331-349 (PDF) | Pozos Privados: Información para los dueños 331-349s (PDF).

Information for Water System Managers

General Sampling Procedure

The provisions of the federal Safe Drinking Water Act requires public water supplies to collect microbiological and chemical samples at various frequencies. This sample collection frequency is determined by each source's water quality history compliance with previous monitoring requirements, and waiver status.

To assist water systems on when to sample and what types of samples to collect, the Office of Drinking water sends out an annual Water Quality Monitoring Reports to Group A systems. Our General Sampling Procedure brochure provides information on how to collect a water sample. Steps and procedures can vary depending on the laboratory that is used so you should follow the instructions that are provided by the laboratory you are using.