Reston Tap Water: From the Potomac to Your Faucet

The Potomac River and the Occoquan Reservoir are where every glass of Reston tap water begins. Between there and your kitchen, the water passes through a treatment plant and a long network of pipes, and each stage leaves its mark on what EWG finds in it.

The bottom line first: Reston's water meets every federal legal limit that applies to it, and the EPA has no violations on file for its supplier. What follows is the journey, step by step, and where each item on the report enters the picture.

1. Two sources: the Potomac and the Occoquan

Reston is served by Fairfax Water, which the EPA lists as the Fairfax County Water Authority. It draws surface water from two places, the Potomac River and the Occoquan Reservoir, and supplies about 1,121,613 people across Fairfax County, Fairfax City and Falls Church City through 281,686 service connections.

Surface water is open to the sky. It carries natural organic matter, along with whatever microbes live in a river or lake. That is normal, and it is why the next step exists. It also matters later, because that organic matter is one ingredient in the byproducts that form in the pipes.

The data in this article covers ZIP codes 20190, 20191 and 20194, plus surrounding Reston areas.

2. The treatment plant

At the plant, the water goes through a series of steps, as listed on the EPA's record:

• Powdered activated carbon
• Coagulation and flocculation, which clump fine particles together
• Rapid sand filtration, which strains those clumps out
• Chloramines for disinfection
• Fluoridation

This process makes the water safe to distribute. It is not designed to remove PFAS, which is why the EPA's monitoring (UCMR5, 2023 to 2025) still found 8 PFAS compounds in this supply. Two of them, PFOA and PFOS, were measured above the 4 ppt federal limit the EPA set in 2024. That limit becomes enforceable in 2029 and is judged on a running annual average, so this is not a violation. EWG links PFOA to harm to the immune system, fetal growth and child development, and increased cholesterol, and PFOS to cardiovascular harm and harm to fetal growth.

3. In the pipes

A system serving more than a million people has a long distribution network, and water can spend days in it before reaching Reston homes. To stay safe the whole way, it carries its disinfectant along.

Fairfax Water uses chloramines rather than free chlorine. Chloramine stays stable over long pipe runs and produces fewer trihalomethanes. The tradeoff is that it is more corrosive to old plumbing.

This is also the stage where disinfection byproducts build up. They are not carried in from the river, and most of them are not made at the plant. As the disinfectant meets the organic matter left in the water, trihalomethanes and haloacetic acids keep forming as the water travels. That explains why the highest readings in a big network can sit well above typical ones. EWG lists total trihalomethanes at up to 75.9 ppb and haloacetic acids (HAA5) at up to 54.1 ppb, which it puts at 300 times its guidelines. EWG links TTHMs to cancer and fetal development effects, and HAA5 to cancer.

None of this argues against disinfection. Keeping germs out of a long pipe network is the whole point, and byproducts are the cost of doing it.

4. At your tap

The last few feet matter more than people expect. Water that left the plant clean can pick up lead from older service lines, solder and fixtures, and chloramine's corrosiveness makes old plumbing the place to watch.

Utilities measure lead at household taps and report the 90th percentile. For Fairfax Water it is 1.2 ppb: nine in ten homes tested came in below that, one in ten above. That is well under the EPA action level of 10 ppb (lowered from 15 ppb, in force November 2027), and 6 times EWG's standard of 0.2 ppb. EWG links lead to harm to the brain and nervous system.

One item on the report does not belong to a single stage: chromium-6. EWG lists an average of 0.10 ppb, 5 times its 0.02 ppb guideline, and links it to stomach cancer.

Reston's numbers at a glance

Contaminant	Found	EWG guideline	Over by
Trihalomethanes	Up to 75.9 ppb	0.15 ppb	300×
Haloacetic acids	Up to 54.1 ppb	0.1 ppb	300×
PFOA	7.4 ppt	0.09 ppt	82×
PFOS	5.7 ppt	0.3 ppt	19×
Lead (90th pct.)	1.2 ppb	0.2 ppb	6×
Chromium-6	0.10 ppb avg	0.02 ppb	5×

"Over by" compares each level with EWG's health guideline, not the federal legal limit, which these levels meet. EWG's standards, updated February 2025, are in its words "based only on protecting health and does not consider technical feasibility or the cost of water treatment." Federal limits also weigh what treatment can achieve and what it costs.

Picking up where the pipes leave off

Because the last step of the journey happens in your own plumbing, your own tap is the best place to measure. Sanavia's free water test is mailed anywhere in the U.S., or done in person in Northern Virginia.

If you choose to treat water at the sink, carbon filters mainly help with taste and odor, and other results vary by product. Under-sink reverse osmosis is a common way to reduce dissolved contaminants, such as disinfection byproducts, at the tap. The Sanavia Hydra is a tankless under-sink RO system. In independent accredited lab testing of an Arlington, VA home's tap water, total trihalomethanes fell from 58 ppb to 2.79 ppb after the Hydra, a 95% reduction. Read the lab report. That was a single home, so it is a reference, not a guarantee for your tap.

The complete breakdown, including every PFAS compound, is in our Reston, VA water quality report.