The tap water supplied to residents in Washington, D.C., meets or exceeds all federal water quality standards. Rigorous treatment and continuous monitoring ensure the water is safe for consumption as it leaves the central distribution system. However, localized issues, particularly those related to aging private infrastructure, mean residents should remain informed about the water’s journey to their individual taps.
How DC Water is Sourced and Treated
The principal source for the District of Columbia’s public water supply is the Potomac River, accounting for nearly all the water delivered. Water is drawn from two intake points at Great Falls and Little Falls by the Washington Aqueduct, operated by the U.S. Army Corps of Engineers. This raw water then enters purification at the Dalecarlia and McMillan treatment plants.
Purification begins with coagulation and flocculation, where chemicals are added to clump suspended particles. These clumps are removed through sedimentation and filtration, passing through layers of material like sand and anthracite coal. The final step is disinfection, typically using chlorine and chloramines to eliminate bacteria and viruses.
A corrosion control agent, orthophosphate, is added before distribution. This substance creates a protective film on the inside of pipes, preventing metals like lead from leaching into the water. Once treated, DC Water purchases the potable water and manages its distribution across the District.
Current Water Quality and Regulatory Status
The safety of DC tap water is overseen by the U.S. Environmental Protection Agency (EPA) under the Safe Drinking Water Act. DC Water consistently reports that the water meets or surpasses all EPA regulatory standards for contaminants. The utility performs extensive monitoring, collecting and testing over 40,000 samples annually from various points in the system, exceeding the required minimum.
The results of this testing are made public each year in the annual Water Quality Report, detailing the levels of all regulated contaminants. This report confirms that common contaminants like bacteria, nitrates, and disinfection byproducts are maintained within legal limits. The water leaving the treatment facility is certified as safe for drinking and all other household uses.
Regulatory compliance focuses on the public water system, ensuring the water is safe as it flows out of the city’s water mains. Localized water quality concerns generally arise after the treated water enters the pipes of private property.
Understanding the Risk of Lead Service Lines
The primary localized threat to water quality comes from aging infrastructure, specifically lead service lines and household plumbing. A lead service line is the pipe segment connecting the public water main to the building’s internal plumbing. Homes built before the 1980s are most likely to have this connection, which is not part of the city’s main distribution system.
Lead contamination occurs when water remains stagnant within these pipes or fixtures, causing the metal to corrode and leach into the water. This risk exists even with the addition of orthophosphate, as the protective coating can be disturbed by changes in water chemistry or stagnation. Disturbing the service line, such as during street work or partial replacement, can temporarily increase the release of lead particles.
DC Water is actively working to remove all lead service lines, recognizing that no level of lead exposure is without risk. The utility offers the Lead Pipe Replacement Assistance Program (LPRAP) and coordinates full pipe replacements during capital improvement projects. Residents can check the material of their service line and are encouraged to participate in these programs to eliminate this potential source of contamination.
Individual Testing and Filtration Options
For residents concerned about lead or other potential contaminants originating from home plumbing, several proactive steps are available. DC Water offers free lead testing kits annually to all residential and commercial customers. These kits allow residents to collect a sample of their tap water, which is then analyzed to determine if lead is present.
Using a certified water filter is an effective measure for reducing localized risk. Filters must be certified to meet the NSF/ANSI Standard 53, which verifies the device’s ability to remove lead. These certified filters are available in various forms, including pour-through pitchers, faucet-mounted filters, and under-sink systems.
Simple behavioral changes can also help mitigate potential exposure. Households should always use cold water for drinking, cooking, and preparing infant formula, as hot water dissolves contaminants more readily. Running the cold water tap for a few minutes before use, especially after stagnation like overnight, helps flush out water sitting in the home’s pipes and fixtures.