What's in Herndon, VA tap water?
Herndon distributes water it buys treated from Fairfax Water, sourced from the Potomac and the Occoquan Reservoir. EWG's testing of Herndon's water flags haloacetic acids, hexavalent chromium and PFAS above health-based guidelines.
Town of Herndon water quality report, explained
What Town of Herndon's own test results show for Herndon, compared with EWG's health guidelines. Every result here is within EPA legal limits.
Served by
Fairfax Water
Potomac River + Occoquan Reservoir
14
over guideline
Zip codes covered: 20170, 20171 and surrounding Herndonareas. “× over” compares the detected level to EWG's health guideline, not the federal legal limit.
Measured by the EPA · Herndon, VA
Herndon, VA tap water is fully legal.
It is also 82× the health standard for PFOA.
Herndon does not treat its own water. It buys finished water from Fairfax County Water Authority and moves it through 5,595 of its own service connections, which is the part that matters for lead: the treatment plant is somebody else's, the pipe running to your kitchen is Herndon's.
River water has to be disinfected hard enough to stay safe across the whole network, and this system uses chloramines rather than free chlorine. Chloramine is more stable in long pipe runs and produces fewer trihalomethanes — but it is more corrosive to old plumbing, which is precisely how lead gets into water that left the plant clean.
Every federal limit that applies here is met. Those limits weigh what removal costs. EWG says its health standards are “based only on protecting health and does not consider technical feasibility or the cost of water treatment”. Here is how far apart the two are.
Harm to the immune system; harm to fetal growth and child development; increased cholesterol · EPA limit 4 ppt (set 2024, enforceable from 2029)— also above this
Cardiovascular harm; harm to fetal growth · EPA limit 4 ppt (set 2024, enforceable from 2029)— also above this
Harm to the brain and nervous system · EPA limit 10 ppb (action level, lowered from 15 ppb, in force November 2027)
Harm to fetal growth and child development · no federal limit exists
Harm to fetal growth and child development · no federal limit exists
Harm to fetal growth and child development · no federal limit exists
Hormone disruption; harm to fetal growth and child development · no federal limit exists
Harm to fetal growth and child development · no federal limit exists
PFOA and PFOS were measured above the federal limits too. Compliance is judged on a running annual average rather than a single sample, so this is not a violation — but it is the number EPA itself set as the line.
The EPA's latest round found 8 PFAS compounds in this supply. Lead sampling put the ninetieth percentile at 0.68 ppb — meaning nine in ten homes tested below that, and one in ten above it. It has no violations on file.
Herndon, Town of, on the EPA's record
- Source
- surface water
- Connections served
- 5,595
- People served
- 24,601
Levels: EPA Fifth Unregulated Contaminant Monitoring Rule (UCMR5, 2023–2025) for PFAS, and the Lead and Copper Rule 90th-percentile result for lead and copper — the highest reported for Fairfax County Water Authority, whose water Herndon, Town of distributes. Health standards: EWG's published drinking water standards, updated February 2025. Levels vary by sampling point and date, and being above a health standard is not a legal violation.
14 contaminants above EWG's health guidelines
Everything EWG found above its guideline in Herndon's water, from testing in 2013-2024. A level can be under the legal limit and still be listed here: EWG's guidelines are set to protect health, not to be easy to meet.
| Contaminant | In this water | EWG guideline | Times over |
|---|---|---|---|
| Haloacetic acids (HAA9) | 18.6 ppb | 0.06 ppb | 310× |
| Total trihalomethanes (TTHMs) | 19.7 ppb | 0.15 ppb | 131× |
| Haloacetic acids (HAA5) | 12.8 ppb | 0.1 ppb | 128× |
| Bromodichloromethane | 4.78 ppb | 0.06 ppb | 80× |
| Trichloroacetic acid | 5.14 ppb | 0.1 ppb | 51× |
| Dichloroacetic acid | 6.50 ppb | 0.2 ppb | 32× |
| Chloroform | 11.8 ppb | 0.4 ppb | 30× |
| Dibromochloromethane | 2.82 ppb | 0.1 ppb | 28× |
| Dibromoacetic acid | 0.704 ppb | 0.03 ppb | 23× |
| Chromium (hexavalent) | 0.169 ppb | 0.02 ppb | 8.4× |
| Nitrate | 1.12 ppm | 0.14 ppm | 8× |
| Nitrate and nitrite | 1.12 ppm | 0.14 ppm | 8× |
| Perfluorooctanoic acid (PFOA) | 0.417 ppt | 0.09 ppt | 4.6× |
| 6:2 Fluorotelomer Sulfonic Acid (6:2 FTSA) | 3.17 ppt | 1 ppt | 3.2× |
Source: EWG Tap Water Database, Town of Herndon (VA6059550).
The fix for Herndon water
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Herndon water quality FAQ
Is Herndon, VA tap water safe to drink?
Water from Town of Herndon meets all federal EPA legal limits. However, independent EWG testing finds 14 contaminants above its stricter health-based guidelines, including haloacetic acids (HAA9) and total trihalomethanes (TTHMs). Legal compliance and health-optimal water are not the same thing.
What contaminants are in Herndon water?
The most notable contaminants above EWG health guidelines are haloacetic acids (HAA9), total trihalomethanes (TTHMs), haloacetic acids (HAA5), bromodichloromethane and 10 more. These are largely disinfection byproducts and trace metals common to the region's water sources.
Does a reverse osmosis system remove these contaminants?
Yes. A reverse osmosis system like the Sanavia Hydra uses a 0.0001-micron membrane plus multi-stage carbon filtration to reduce every contaminant class detected in Herndon water, at your tap, regardless of what the utility does upstream.
The contaminants flagged in Herndon water
Plain-English guides to what Fairfax Watertesting turns up above EWG's health guidelines — what each one is, and what actually removes it.
Reverse osmosis in Herndon, VA
Fairfax Water treats this water to the federal standard, yet the contaminants listed above still exceed EWG’s stricter health guidelines — Haloacetic acids (HAA9), Total trihalomethanes (TTHMs), Haloacetic acids (HAA5) and 11 more. Most of them either pass straight through treatment or form after the plant, in the pipes between it and the tap, which is why the fix has to be at the tap as well.
PFAS is the reason a carbon pitcher is not enough here. The compounds do not break down, they are measured in parts per trillion, and the federal limit that covers them is not enforceable until 2029. A reverse osmosis membrane is one of the few things at household scale that reduces them rather than passing them through.
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