Background on Fairfax County Water Supply and PFAS Monitoring
The Fairfax County Water Authority provides water to over 1.1 million people through nearly 282,000 connections, sourcing its water from surface water supplies. To monitor for per- and polyfluoroalkyl substances (PFAS), a federal survey called the Unregulated Contaminant Monitoring Rule (UCMR5) is conducted, providing occurrence data but not compliance enforcement. These data reflect the system's water as it leaves the treatment plant, not the conditions inside individual homes or plumbing systems.
Why PFOA and PFOS Are Measured in Nanograms per Litre
Understanding the Measurement Scale
PFAS concentrations in Fairfax's water are reported in nanograms per litre (ng/L), equivalent to parts per trillion (ppt). This unit measures extremely small quantities—one nanogram per litre represents one trillionth of a gram in a litre of water. Four decimal places reflect very precise laboratory capabilities necessary for detecting these "forever chemicals" at trace levels.
Levels Detected in Fairfax Water
- PFOA: Detected in some samples at a highest value of 0.0074 µg/L (7.4 ng/L), with a median detected value around 0.0061 µg/L (6.1 ng/L)
- PFOS: Detected at highest 0.0057 µg/L (5.7 ng/L), median detection near 0.0052 µg/L (5.2 ng/L)
- Other measured PFAS compounds have detections below or near these levels, with no detections for certain compounds
The federal maximum contaminant levels (MCLs) set in 2024 for PFOA and PFOS are 4 ng/L each. While some measured values exceed these MCLs, the UCMR5 sampling is not a compliance test and these detections do not indicate violations or unsafe water. The system has no health-based violations on record.
Explaining the Hazard Index for Newer Fluorinated Compounds
Mixtures of Fluorinated Compounds
Alongside PFOA and PFOS, newer PFAS compounds such as PFHxS, PFNA, HFPO-DA, PFBS, PFHxA, PFPeA, PFBA, and PFHpA were also monitored. The hazard index concept considers combined effects but does not imply health risk without specific toxicological interpretation. Many of these compounds were not detected or were found at very low levels.
Implications of Hazard Index Data
The presence of multiple fluorinated compounds, detected at trace concentrations, underscores the complexity of PFAS monitoring and the need for detailed water testing at the household level to fully understand water quality for individual residences.
Household Symptoms That May or May Not Indicate PFAS Presence
What to Observe
- PFAS compounds are tasteless and odorless; they do not cause visible staining or typical water quality symptoms like cloudiness or unpleasant taste
- Household complaints such as unusual taste or odor likely stem from other water quality factors, not PFAS
- Health concerns related to PFAS require professional water testing and interpretation, as no sensory symptoms reliably indicate presence
What Symptoms Do Not Point to PFAS
- Water hardness-related scaling or soap inefficiency is unrelated to PFAS
- Discoloration or sediment is generally due to mineral content or plumbing materials, not PFAS
The Role of Plumbing Material and Age in Water Quality
Difference Between Source Water and Plumbing Effects
PFAS data originate from treated surface water at the system level. However, household plumbing materials and the age of piping can influence water quality inside the home by contributing metals, sediment, or biofilm that are not related to PFAS levels.
Testing for Household-Specific Conditions
To understand the presence of PFAS specifically in your home's water, you would need to independently test your tap water, as system-level data do not account for changes caused by plumbing. Plumbing material choices do not affect PFAS concentrations directly but may affect other water qualities.
Considerations for Large or Seasonal Households
Water Quality Dynamics
Larger households or those with multiple properties in Fairfax County might experience different water usage patterns, including stagnation in pipes during low-use periods, which can alter some water characteristics but not PFAS levels from the source.
Implications for Water Treatment Choices
If water is unused for extended periods, flushing and testing become important to assess current conditions. Seasonal properties might require specific attention to maintaining water quality through periodic monitoring.
Conclusion
Fairfax County's water system monitoring shows that PFAS compounds, including PFOA and PFOS, are detected at trace levels measured in nanograms per litre, with no health-based violations recorded. Understanding what these measurements mean, the influence of household plumbing, and user scenarios is vital for deciding on water treatment options.
When choosing equipment to address PFAS, the C-Series PFAS Forever Chemicals Filter offers a documented technology to reduce these compounds at the point of use. This system ships ready to configure and provides an option for those prioritizing PFAS reduction at home.
Where this information comes from
Source: EPA SDWIS public water system record. Sampled 2025-02-13. These figures describe the public water system's record, not the plumbing inside any individual building.
On record: EPA UCMR5 monitoring (2023-2025) for FAIRFAX COUNTY WATER AUTHORITY (VA6059501), VA: 240 results across 10 listed contaminants, 36 detections above the reporting level; 5 results above a 2024 federal MCL