About Drinking Water Quality in Washington, D.C.

The delivery of safe, clean, high-quality drinking water is one of DC Water's highest priorities. Drinking water in the District of Columbia comes from the Potomac River. The U.S. Army Corps of Engineers, Washington Aqueduct (Aqueduct), is a federally owned agency responsible for treating the drinking water. DC Water purchases the water from the Aqueduct and delivers it to residents and businesses throughout the city.

Drinking Water Treatment and Distribution

Water Treatment Process

Treatment Process

The Aqueduct draws water from the Potomac River at the Great Falls and Little Falls intakes and treats the water at two treatment plants, Dalecarlia and McMillan. The Aqueduct filters and disinfects water from the Potomac River to meet safe drinking water standards. The treatment process includes sedimentation, filtration, fluoridation, pH adjustment, primary disinfection using free chlorine, secondary disinfection with chloramine through the addition of ammonia, and corrosion control with orthophosphate. For more information on the drinking water treatment process, visit the Aqueduct's website.

Distribution System

DC Water purchases water from the Aqueduct and is responsible for maintaining the distribution system that delivers drinking water to customers. DC Water maintains over 1,300 miles of pipe and distributes drinking water to more than 600,000 residents and businesses in the District of Columbia.

Water Distribution System
Diagram of Water Distribution System

The DC Water distribution system begins at the water treatment plant and ends at your private service lines. Customer service lines connect to the mains in the streets and deliver water to residents and commercial buildings, eventually reaching your taps. Water is continuously moving through our distribution system, typically at a high water flow that keeps the water fresh. However, once the water leaves the main and enters a customer's service line, the flow of water is dependent on your individual water usage. When water is not in use for several hours or days, water quality can deteriorate.

DC Water recommends running the cold water tap for at least two minutes when it has not been used for several hours. This will flush the stagnant water from the service lines and bring fresh water in from the fast-flowing mains.

Drinking Water Regulations and Standards

The U.S. Environmental Protection Agency (EPA) is responsible for establishing water quality standards that are protective of public health. DC Water delivers drinking water that meets EPA regulatory standards and surpasses these standards to meet more stringent water quality targets established by DC Water.

EPA Regulations

The Safe Drinking Water Act (SDWA) was passed by Congress in 1974 and amended in 1986 and 1996. SDWA is the federal law that regulates treatment and water quality standards for drinking water in the United States. The EPA sets health-based standards to protect against contaminants that may be found in drinking water. DC Water is required to comply with these regulations and must routinely report water quality test results to the EPA and the public.

DC Water Target Levels

DC Water is committed to providing customers with the highest quality drinking water and continuously works to deliver water that goes beyond federal standards. DC Water accomplishes this goal by aiming to meet target levels that are stricter than water quality standards required by EPA. DC Water regularly collects tap water samples throughout the District of Columbia to ensure the drinking water meets these more stringent water quality targets.

DC Water's Role in Water Quality

DC Water has a dedicated Drinking Water Division that collects and analyzes water samples throughout the District of Columbia on a daily basis. These monitoring programs include sampling and analyses that are required by EPA and additional sampling programs conducted voluntarily by DC Water.

Federally Required Sampling Programs

DC Water conducts compliance monitoring on a daily basis to ensure water quality meets EPA standards. Water quality technicians collect and analyze samples for lead and copper, total coliform (bacteria) and disinfection byproduct levels. Compliance monitoring ensures that drinking water treatment effectively prevents pipe corrosion, removes bacteria and other contaminants, and minimizes potentially harmful treatment byproducts. Visit Water Quality Test Results to view monthly monitoring reports.

DC Water Voluntary Sampling Programs

DC Water operates voluntary sampling programs to support our commitment to providing high-quality drinking water to our customers. Water quality technicians collect and analyze hundreds of water samples per month throughout the District of Columbia. The Drinking Water Division responds quickly to customer complaints and conducts water quality monitoring among the city's most vulnerable populations. DC Water operates two mobile laboratories that allow technicians to conduct on-site water quality tests and respond to emergencies.

DC Water is committed to providing reliable service and delivering water that meets or surpasses national water quality standards. Our Customer Complaint Program ensures that DC Water responds to and investigates water quality issues when they are reported by customers. Water quality technicians regularly visit customer homes to collect and analyze tap and hydrant samples. DC Water works closely with customers to address concerns and resolve water quality issues in a timely manner.

In addition to the Customer Complaint Program, DC Water conducts routine monitoring in schools and daycare centers throughout the city. This sampling program ensures that schools and daycare centers are providing clean, safe drinking water to the city's most vulnerable populations. Water quality technicians collect approximately 700 samples a year and provide guidance to schools and daycares for maintaining high water quality.

DC Water Flushing Program

DC Water is continuously maintaining and improving the distribution system to provide clean, safe, high-quality drinking water. The Drinking Water Division monitors a regular flushing program to clean the mains in the streets throughout the District of Columbia. DC Water's distribution system contains many pipes made of iron. Although iron in drinking water is not a risk to human health, buildup of this material may cause discolored tap water. The flushing program aims to prevent issues of discoloration and minimize the presence of iron in the distribution system.

Where To Find Information On Water Quality

DC Water reports monthly test results for certain water quality parameters in the Water Quality Test Results section of the website. In addition, the DC Water Annual Water Quality Report is mailed to all addresses within our distribution system, whether or not a water bill is delivered to the address. The annual report includes the results from all water quality tests conducted in the past year. You can also view the latest Annual Water Quality Report and reports from previous years on the website.

If you have questions or concerns regarding the quality of your water, please contact the Drinking Water Division at drinkingwater@dcwater.com or 202-612-3440 (M-F, 8 a.m. - 4:30 p.m.) or the 24-hour Command Center at 202-612-3400.

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