Backflow News
DC Water Issues Boil Water Advisory for Entire District of Columbia Following Treatment Plant Reduction — Cross-Connection Risks During Pressure Events
On July 3, 2024 — the eve of Independence Day — DC Water issued a Boil Water Advisory for all customers in the District of Columbia, as well as for the Pentagon, Arlington National Cemetery, and Reagan National Airport. The advisory, which affected hundreds of thousands of people and came just hours before a major national holiday, was triggered not by a confirmed contamination event but by a significant pressure reduction event in the water system — exactly the kind of pressure disruption that creates elevated backflow risk across a distribution system’s entire service area.
What Triggered the Advisory
DC Water was notified on the afternoon of July 3, 2024, by the Army Corps of Engineers’ Washington Aqueduct that due to elevated turbidity in source water, the Dalecarlia Water Treatment Plant had been forced to reduce production. All water treatment operations were being conducted at the McMillan Treatment Plant while Dalecarlia was offline. The shift in treatment load created a pressure reduction event in DC Water’s distribution system — a drop in the pressure that normally keeps water flowing in the correct direction from the treatment plant outward to customers, and that provides the positive pressure barrier against backflow from cross-connected non-potable sources.
DC Water stated clearly: ‘We have no information that the water was contaminated by this incident, but we issue this advisory as a precaution while we test the water.’ The utility’s caution was appropriate and reflects standard emergency response practice: when a significant pressure reduction event occurs in a distribution system, the risk that backsiphonage has pulled contaminants from cross-connected sources into the supply is real, even if unconfirmed. Every minute the system is under reduced pressure is a minute during which any unprotected cross-connection — any irrigation system, boiler connection, fire suppression system, or industrial connection without an appropriate and functioning backflow preventer — represents a potential entry point for contamination.
The Scope and Logistics
The advisory covered the entire DC Water service area — the District of Columbia, the Pentagon, Arlington National Cemetery, and Reagan National Airport. Customers were directed to boil water before using it for drinking, brushing teeth, preparing food, washing fruits and vegetables, preparing infant formula, making ice, washing dishes by hand, and giving water to pets. They were specifically told not to use home filtering devices in place of boiled or bottled water. The advisory remained in effect until DC Water’s testing confirmed the water supply had returned to normal production and met water quality standards.
DC Water provided customer contact information through multiple channels: Customer Service at (202) 354-3600 during business hours, the 24-Hour Command Center at 202-612-3400 for after-hours inquiries, and dcwater.com for updates. The utility also issued bilingual FAQs in English and Spanish, and the advisory materials were available in multiple languages through dcwater.com/boilwaterFAQ. The scope of the advisory — reaching every federal facility served by DC Water along with hundreds of thousands of District residents — reflected the scale of the pressure event and the precautionary principle that governs responsible water system emergency response.
Why Pressure Events Are Cross-Connection Events
The DC Water advisory is a useful case study for understanding why pressure reduction events and backflow risk are directly linked. Under normal operating conditions, the positive pressure in a distribution system keeps water flowing in one direction: from the treatment plant outward to every faucet, fixture, and connection. That positive pressure is also what keeps contaminants from cross-connected sources out of the potable supply — as long as the distribution system pressure exceeds the pressure in any connected non-potable system, flow direction is maintained and backflow does not occur.
When distribution system pressure drops — as a result of a treatment plant going offline, a major main break, an unusually high demand event like firefighting operations, or a pump failure — that pressure differential can reverse. Any cross-connection that is protected only by a failed or absent backflow preventer becomes a potential contamination entry point in that window. This is precisely why every state cross-connection control program requires that backflow preventers be installed at all identified cross-connections — not just the ones that are easily visible, not just the ones that are obviously hazardous, but all of them. A pressure drop event makes every unprotected cross-connection a simultaneous active risk.
The Importance of Annual Testing in Context
The DC Water advisory is also a reminder of why annual testing is not bureaucratic redundancy — it is the only mechanism for confirming that the assemblies installed throughout the distribution system’s customer base are actually functioning as designed. A backflow preventer that passed its test three years ago but has since experienced internal wear, check valve seat deterioration, or corrosion may not respond correctly when called upon during a pressure event. Annual testing catches failing assemblies before they fail in service — before the pressure event that tests every assembly simultaneously whether a scheduled test is due or not.
In DC’s case, no confirmed contamination was attributed to the July 3 event, and the advisory was lifted once testing confirmed water quality had been restored. But the event underscores that the Washington DC metropolitan area — served by a system of multiple treatment plants, complex pressure zones, and thousands of commercial, institutional, governmental, and multi-family connections — depends on the functioning of every backflow preventer in its distribution area to maintain water quality during abnormal pressure conditions. The city’s cross-connection control program covers the District’s commercial, institutional, and multi-unit residential connections. The most important safeguard during an event like July 3 is the network of properly installed, properly maintained, annually tested backflow prevention assemblies that serve as the last line of defense between the distribution system and every potential contamination source it passes.
Pressure Events and Backflow: What Property Owners Should Know
Boil water advisories issued following pressure reduction events are not only about whether the water received was contaminated — they are also about whether every backflow preventer in the affected system functioned correctly during the event. The safest position for a DC-area commercial or institutional property owner is one where your backflow assembly is currently tested, on record with DC Water’s cross-connection control program, and confirmed to be functioning. If your assembly is overdue for testing, schedule it now — not after the next pressure event.
Source: DC Water — Official Boil Water Advisory Press Release, July 3, 2024 (dcwater.com); DC Water — Backflow Prevention Devices program page (nyc.gov for NYC context; DC Water direct communications). Published at getyourbackflowtested.com/backflow-news