Surface Water Treatment

What is the best source of water for a public drinking water system?

Without extensive treatment provisions, the use of a properly constructed well that taps a protected groundwater aquifer is the safest source of drinking water. A connection with another public water system that meets all drinking water standards is also a good option. Water that is open to the atmosphere and vulnerable to surface water runoff is not safe to drink without complete treatment. Sources at risk include lakes, rivers, streams and improperly constructed springs. Shallow or poorly constructed wells may also be unsafe.

Why do surface water sources need special treatment to make them safe?

Surface water sources are open to contamination from human and animal waste and other pollution. Consequently, they are particularly susceptible to contamination by organisms such as bacteria, viruses, and parasites that can cause serious illness and disease. Two parasites that cause waterborne illness are Giardia and Cryptosporidium. Giardia is the cause of an illness commonly known as "backpacker's disease." Cryptosporidium is the organism that caused over 400,000 illnesses and 100 deaths in Milwaukee, Wisconsin in 1993.

What special requirements are surface water systems subject to?

Public water systems with surface water sources are subject to extensive federal and state requirements to protect public health. Group A surface water sources are subject to requirements identified in Part 6 of Chapter 246-290 WAC. This regulation complies with the federal Surface Water Treatment Rule and includes filtration, disinfection, operating, monitoring, and reporting requirements. There is no regulation covering existing Group B surface water sources and new Group B surface water sources cannot be approved under chapter 246-291 WAC.

What treatment is required for surface water sources?

Studies of waterborne disease outbreaks have shown that properly designed and operated treatment systems, which include both filtration and disinfection, are effective in preventing waterborne illness.

If surface water is not adequately treated, what is a public water system's responsibility to inform the people who drink it?

Everyone who might use the water needs to be told that it is not safe to drink. The system must give written notice to every user and repeat it every three months. All new users must be informed immediately.

Where can I get help to upgrade my system?

Department of Health staff can answer questions and provide further technical assistance on surface water issues. Surface water treatment systems must be designed by a licensed professional engineer with specific experience in this type of water treatment. (See "More information and assistance," below.)

Once I get the necessary treatment installed, how can I make sure the system runs properly?

To be effective, a treatment system must be properly operated and maintained. State certification for this type of operation and maintenance is required. In some areas of the state there are also certified operators available to perform these services under contract.

Surface Water Treatment Resources


Process Monitoring



Management and Operations

More Information and Assistance

Office of Drinking Water's Regional Offices

Office of Drinking Water 360-236-3100 or toll-free number 800-521-0323

Visit our Operator Certification Program webpage to find information on available training, how to become a certified operator, and certified contract operators.

U.S. Environmental Protection Agency

Safe Drinking Water Hotline 1-800-426-4791

More Surface Water Treatment Resources