Where does Arlington VA get its drinking water?

Arlington buys finished drinking water from the Washington Aqueduct, a division of the U.S. Army Corps of Engineers, which draws Potomac River water at Great Falls and Little Falls and treats it at the Dalecarlia plant in Washington DC. The Aqueduct's three wholesale customers are the District of Columbia, Arlington County and the City of Falls Church. Arlington then distributes that water through roughly 500 miles of its own pipe.

Is Arlington VA tap water safe to drink?

Arlington's water meets federal drinking water standards. Nine contaminants sit above the stricter health guidelines used by independent researchers, led by disinfection byproducts. Total trihalomethanes measure about 47.3 ppb against a legal limit of 80, which is fully legal and roughly 315 times the health guideline. Legal and above the guideline are both true at once.

Why does Arlington water have high disinfection byproducts?

Trihalomethanes and haloacetic acids form when chlorine reacts with natural organic matter carried by a river source. A Potomac supply, mandatory disinfection and long transmission distance produce them by design, which is why they dominate the reports of nearly every Potomac system in the region.

Does Arlington have lead in its water?

Lead does not come from the Washington Aqueduct's treated water. It enters from lead service lines, older solder and brass fixtures on individual properties, so it varies house by house and can only be answered by testing at your own tap.

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Arlington's water comes from a federal plant in DC

The county runs the pipes. The Army Corps runs the treatment. That explains most of what is on an Arlington water report.

Arlington County does not treat its own drinking water. It buys it, already treated, from a federal plant in the District of Columbia. That one fact explains most of what shows up on an Arlington water report, including why Arlington's numbers look so much like DC's, and why the two places once spent the same weekend under the same boil-water advisory.

Where Arlington's water actually comes from

The Washington Aqueduct, a division of the U.S. Army Corps of Engineers, draws Potomac River water at Great Falls and Little Falls and treats it at the Dalecarlia plant in Washington. Congress authorised the Corps to supply Arlington back in 1926, and the arrangement has held ever since. The Aqueduct has exactly three wholesale customers: the District of Columbia, Arlington County, and the City of Falls Church.

Arlington's own utility then moves that finished water through roughly 500 miles of pipe to about 240,000 people. So the county runs the distribution system, sets the rates, and maintains the mains, but the treatment decisions that determine what is in the water are made at a federal plant across the river.

This is why Arlington and DC track each other. When the Potomac had an algae event in July 2024, the advisory that followed covered the District and Arlington together, because it was the same water from the same plant. Shared source, shared plant, shared outcome.

What is actually in it

From the utility's own published testing, compiled in the EWG Tap Water Database as of June 2026, nine contaminants in Arlington's water sit above the health guideline researchers use. The largest are all in one family:

Haloacetic acids (HAA9): 36.8 ppb, about 613 times the health guideline. There is no federal legal limit for the HAA9 group at all.
Total trihalomethanes (TTHMs): 47.3 ppb, about 315 times the health guideline. The legal limit is 80 ppb, so this is comfortably legal.
Haloacetic acids (HAA5): 29.6 ppb, about 296 times the guideline. Legal limit 60 ppb.

Look at the TTHM line again, because it is the clearest example of the thing this whole site exists to point out. 47.3 is legal. The limit is 80. And it is roughly 315 times what independent researchers consider protective for a lifetime of drinking. Nothing is being hidden and nobody is breaking a rule. The rule and the health guideline are simply two different numbers, and the legal one has not moved in decades.

The full Arlington readout, contaminant by contaminant, shows all nine with both benchmarks side by side.

Why a Potomac system produces these specific chemicals

Trihalomethanes and haloacetic acids are disinfection byproducts. They form when chlorine, which is doing the essential job of keeping the water safe from bacteria on its way to you, reacts with natural organic matter that a river carries. A river source plus long transmission plus mandatory disinfection produces them by design. That is why they dominate the reports of nearly every Potomac system in this region, from DC Water to Fairfax Water to Loudoun Water.

The trade is real and it is not close: the alternative to disinfection is waterborne disease. What TTHMs are and where they come from covers the chemistry.

What an Arlington homeowner can actually do

For the byproducts, a carbon filter at the tap handles chlorine taste and some of the byproducts, and Reverse Osmosis (RO) is the more thorough answer for drinking water.
For lead, remember that it does not come from the Aqueduct. It comes from service lines and fixtures inside the property, so it is a per-house question. Arlington's housing stock includes plenty of homes old enough for it to matter. Why lead is a plumbing question, not a utility one.
For hardness, Potomac water runs moderately hard, which is a wear problem for your water heater rather than a health one.
Not a water softener, if the byproducts are what concern you. A softener does nothing for them.

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See Arlington's numbers for yourself

Every figure above comes from testing Arlington already publishes. Type your ZIP and see it laid out: what is above the health guideline, by how much, and what actually addresses each one. Free, no login.

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Go deeper: the full Arlington readout · Alexandria, next door, is run for profit · Loudoun and the data centers · TTHMs explained · why the water smells like a pool some weeks