Loudoun County, Virginia: drinking water report. Loudoun County in northern Virginia has about 420,000 residents, making it one of the wealthiest and…
Loudoun County in northern Virginia has about 420,000 residents, making it one of the wealthiest and fastest-growing counties in the country. Loudoun Water draws from the Potomac River and a network of water reclamation facilities. The county's western half remains agricultural (horse farms, vineyards, cattle), while the eastern half is dense suburban development anchored by the Dulles Technology Corridor.
Washington Dulles International Airport – one of the busiest airports on the East Coast – sits in the heart of Loudoun County. AFFF firefighting foam use at Dulles has been documented, and Virginia DEQ's 2024 PFAS investigation found PFOS at 14 ppt in monitoring wells downgradient from the airport. The contamination affects groundwater in the Broad Run watershed area.
The county's karst limestone geology in the western portion creates rapid contamination pathways. A 2024 VDH private well testing program found that 9% of wells in the western Loudoun karst zone exceeded the nitrate MCL, driven by horse farm and agricultural activity. Loudoun Water's municipal supply from the Potomac meets all standards.
Loudoun County's split between suburban east and rural west creates different water quality profiles. Eastern residents on Loudoun Water benefit from treated Potomac River supply. Western residents on private wells face karst geology risks and should test for nitrate and bacteria regularly.
Check your water for data at your address. For well owners, reverse osmosis handles nitrate and PFAS together. For municipal water users, a carbon filter addresses taste and disinfection byproducts. Our water filter guide covers both scenarios. Pull your detailed report for local data, and visit our Virginia page for statewide patterns.
Drinking water is one exposure route. These federal datasets also cover Loudoun County, VA.
The EPA places Loudoun County, VA in Zone 2 - a moderate-risk category, with a predicted average indoor radon level between 2 and 4 pCi/L. Zone maps predict an area's radon potential from geology and existing indoor readings; they say nothing about a specific house. Testing is the only way to know your own level.
14% of homes in Loudoun County, VA were built before 1980, and 3% before 1950. Residential lead paint was banned in 1978, so housing age is the strongest available proxy for lead-paint exposure. This describes the county's housing stock, not any one home.
Modelled annual fine-particle pollution (PM2.5) in Loudoun County, VA averages 7.5 µg/m³, within the EPA's annual standard of 9 µg/m³. These are CDC modelled county estimates rather than readings from a specific monitor.
How radon zones work · Air quality by county · Lead exposure guide
17 public water systems serving Loudoun County, VA have EPA lead testing on record. The reported lead sample skews toward systems that already flagged a problem, so its exceedance rate is not directly comparable with other areas. 4 water systems serving Loudoun County, VA carry a health-based EPA Safe Drinking Water Act violation.
| Most-cited violation type | Systems affected |
|---|---|
| Lead and Copper Rule | 2 |
| Stage 1 Disinfectants and Disinfection Byproducts Rule | 2 |
| Gross Alpha (excl. radon & uranium) | 1 |
| Combined Radium (226 + 228) | 1 |
| Surface Water Treatment Rule | 1 |
Source: EPA Lead and Copper Rule 90th-percentile tap sampling and EPA SDWIS Safe Drinking Water Act enforcement records, aggregated from the public water systems serving this county. Figures are counts of water systems, not a test of any individual home or tap.