Loudoun's water, the data centers, and what is in your tap
Forty data centers run on recycled water. Your tap runs mostly on water bought from Fairfax. Both facts are worth knowing.
The most common question in Loudoun is whether the data centers are drinking the county's water. The short answer: about forty of them are cooled with recycled wastewater instead, roughly 700 million gallons a year that never had to be drinking water in the first place. The longer answer is more interesting, and it starts with where Loudoun's tap water actually comes from.
Loudoun mostly buys its water
Loudoun Water serves around 320,000 people, and the majority of what comes out of their taps is purchased from Fairfax Water, on the order of 18 million gallons a day. That water is Potomac River water, treated by Fairfax Water and delivered wholesale. Loudoun's own supply, the Goose Creek and Beaverdam reservoirs, backs that up and covers part of the demand.
This matters for reading your report. Much of what shows up in Loudoun's numbers is inherited from the same Potomac treatment that produces Fairfax Water's profile, which is why the two look like relatives.
The data centers, and the water they do not use
Loudoun is Data Center Alley, and the water question is real. What is less well known is the plumbing built to answer it. Loudoun Water's Broad Run Water Reclamation Facility produces highly treated reclaimed water and pipes it to data centers for cooling. In 2025 that system delivered more than 750 million gallons, and roughly forty data centers now run on it rather than on drinking water.
Two things follow, and both are true:
- Every gallon of reclaimed water used for cooling is a gallon of treated drinking water that stayed in the drinking water system, and a gallon of nutrients that did not go into the Potomac and the Chesapeake Bay.
- The reclaimed network only reaches where the pipe reaches. Data centers outside it still buy potable water, and that demand has been growing faster than the reclaimed system can extend.
What is actually in Loudoun's tap water
From Loudoun Water's own published testing, compiled in the EWG Tap Water Database as of June 2026, nine contaminants sit above the health guideline, and the top of the list is the same family that dominates every Potomac system in this region:
- Haloacetic acids (HAA9): 33.1 ppb, about 552 times the health guideline, and there is no federal legal limit for the HAA9 group at all.
- Total trihalomethanes (TTHMs): 41.8 ppb, about 279 times the guideline, against a legal limit of 80 ppb.
- Haloacetic acids (HAA5): 26.5 ppb, about 265 times the guideline, against a legal limit of 60 ppb.
Read the TTHM line the way it deserves: 41.8 is roughly half the legal limit, and roughly 279 times the level independent researchers call protective. Both statements describe the same glass of water. The full Loudoun readout shows all nine against both benchmarks.
These are disinfection byproducts: what forms when the chlorine that keeps the water safe on its journey reacts with organic matter a river carries. A surface water source and a long distribution system produce them. The alternative to disinfecting is not a cleaner glass, it is waterborne disease.
What a Loudoun homeowner can do about it
- For the byproducts, carbon filtration helps with taste and some of the compounds; Reverse Osmosis (RO) at the kitchen tap is the thorough answer for drinking water.
- For hardness, Potomac water runs moderately hard, which is a water heater and fixture problem rather than a health one. Loudoun's newer housing stock means a lot of relatively young heaters that are worth protecting early.
- For lead, it does not arrive from Fairfax Water or from Goose Creek. It comes from the plumbing in an individual house, so it is a per-address question: how to test your own tap.
See Loudoun's numbers for yourself
Everything above comes from testing Loudoun Water 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.
See my water report →Prefer to talk to a person? Call or text (571) 396-0299.
Go deeper: the full Loudoun readout · where Arlington's water comes from · Fairfax Water and PFAS
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