Data & Methodology — Washington County

Full contaminant data, sample history, and sourcing for Washington County. For readers who want to go beyond the summary.

Contaminant Data — All Analytes

122 well testing events on record, covering 20 analytes. Data spans 1926 to 2024.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. PA Avg
Iron 103 1926–1999 99%
73% of limit ↓ 87% below
Manganese 92 1967–1999 88%
20% of limit ↓ 96% below
Arsenic 14 1983–1999 86%
30% of limit ~ typical
Sulfate 102 1926–1999 100%
22% of limit ↑ 27% above
Lead 14 1983–1999 14%
670% of limit ↑ 14385% above
Nitrate 17 1926–1999 65%
2% of limit ↓ 90% below
Chloride 102 1926–1999 100%
8% of limit ↓ 23% below
Fluoride 90 1971–1999 93%
5% of limit ~ typical
HFPO-DA (GenX) municipal 13 2023–2025 0%
— —
Nitrite 6 1992–1999 0%
— —
PFHxS municipal 10 2023–2025 0%
— —
PFNA municipal 10 2023–2025 0%
— —
PFOA municipal 17 2023–2025 18%
52% of limit ↓ 44% below
PFOS municipal 17 2023–2025 6%
14% of limit ↓ 89% below
Radon 1 1997 100%
7% of limit ↓ 95% below
Uranium 5 1997–1999 80%
1% of limit ↓ 57% below
Hardness 102 1926–1999 100%
— ↑ 57% above
PFBS municipal 13 2023–2025 0%
— —
pH 94 1967–2023 100%
— ~ typical
Sodium 101 1926–1999 100%
— ↑ 83% above

Distribution shows the share of samples in each concentration band relative to the EPA Maximum Contaminant Level (MCL): Low = below half the MCL, Moderate = between half and the MCL, High = above the MCL. Analytes without an MCL (e.g. sodium, pH) show — in the limit columns. State average is based on county median values across PA.

Compare your result with Washington County

Of the 102 chloride tests on record for Washington County (1926–1999), 0% found none, and half were below 20.5 mg/L.

Of the 90 fluoride tests on record for Washington County (1971–1999), 7% found none, and half were below 200 µg/L.

Of the 103 iron tests on record for Washington County (1926–1999), 1% found none, and half were below 220 µg/L.

Of the 92 manganese tests on record for Washington County (1967–1999), 12% found none, and half were below 10 µg/L.

Of the 102 sulfate tests on record for Washington County (1926–1999), 0% found none, and half were below 54.5 mg/L.

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Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • Iron 103 samples
  • Manganese 92 samples
  • Sulfate 102 samples
  • Nitrate 17 samples
  • Chloride 102 samples
  • Fluoride 90 samples
  • PFOA 17 samples
  • PFOS 17 samples
  • Hardness 102 samples
  • pH 94 samples
  • Sodium 101 samples

Limited data (<15 samples) — interpret with caution

  • Arsenic 14 samples
  • Lead 14 samples
  • HFPO-DA (GenX) 13 samples
  • Nitrite 6 samples
  • Radon 1 sample
  • Uranium 5 samples
  • PFBS 13 samples

Public vs. Private Water in Washington County

31 Active public water systems
46,206 Residents on public water
31% Households on private wells

Public water systems in Washington County are regulated by the EPA and must test and report contaminant levels. Private well owners are responsible for their own testing — there is no routine monitoring of private wells by any government agency.

CDC Health Outcome Correlations

Where contaminants detected in Washington County have established associations with specific health outcomes, we cross-reference CDC PLACES county-level prevalence data. This is a contextual signal, not a causal claim.

Contaminant Associated Condition Washington County Prevalence PA Average Source Year
Lead Heart disease rate 7.6% 7.2% 2020
Arsenic Cancer prevalence 6.1% 7.0% 2020
Arsenic Kidney disease rate 2.4% 3.0% 2020

Source: CDC PLACES county-level estimates. Raw data: Download Washington County CDC PLACES data →

Data Sources

This report aggregates data from the following public databases:

Methodology

Raw records are downloaded from the Water Quality Portal and normalized to µg/L (ppb). Records are deduplicated by sample ID and date, and certified outliers are excluded. Analyte names are mapped to EPA canonical forms. Detection rates, distribution bands, and MCL comparisons are computed from the normalized dataset.

Distribution bands use the EPA Maximum Contaminant Level as the threshold: concentrations below 50% of the MCL are classed as Low, between 50% and 100% as Moderate, and above 100% as High. For analytes without an MCL (sodium, hardness, pH), distribution is not computed.

State comparison uses the median of county median values across all counties in PA with at least one sample for that analyte.

Last updated: 2026-08-04

Full methodology →