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

389 well testing events on record, covering 18 analytes. Data spans 1942 to 2019.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. TX Avg
Manganese 81 1939–2020 65%
124% of limit ↑ 93% above
Nitrate 130 1939–2005 98%
20% of limit ~ typical
Iron 121 1939–2020 78%
33% of limit ↓ 78% below
Arsenic 50 1992–2020 42%
68% of limit ↑ 78% above
Chloride 170 1939–1980 100%
16% of limit ↓ 56% below
Sulfate 169 1939–1980 100%
6% of limit ↓ 80% below
Fluoride 314 1939–2020 98%
8% of limit ↓ 69% below
HFPO-DA (GenX) municipal 6 2023 0%
— —
Lead 50 1992–2020 4%
43% of limit ↑ 157% above
PFHxS municipal 6 2023 0%
— —
PFNA municipal 6 2023 0%
— —
PFOA municipal 6 2023 0%
— —
PFOS municipal 6 2023 0%
— —
Uranium 9 2009–2020 11%
4% of limit ↓ 77% below
Sodium 137 1939–1980 100%
— ↓ 59% below
pH 66 1939–1980 100%
— ~ typical
PFBS municipal 6 2023 0%
— —
Hardness 137 1939–1980 100%
— ~ typical

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 TX.

Compare your result with Washington County

Of the 50 arsenic tests on record for Washington County (1992–2020), 58% found none.

Of the 170 chloride tests on record for Washington County (1939–1980), 0% found none, and half were below 39 mg/L.

Of the 314 fluoride tests on record for Washington County (1939–2020), 2% found none, and half were below 300 µg/L.

Of the 121 iron tests on record for Washington County (1939–2020), 22% found none, and half were below 70 µg/L.

Of the 50 lead tests on record for Washington County (1992–2020), 96% found none.

Of the 81 manganese tests on record for Washington County (1939–2020), 35% found none, and half were below 20 µg/L.

Of the 130 nitrate tests on record for Washington County (1939–2005), 2% found none, and half were below 1.72 mg/L.

Of the 169 sulfate tests on record for Washington County (1939–1980), 0% found none, and half were below 14 mg/L.

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Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • Manganese 81 samples
  • Nitrate 130 samples
  • Iron 121 samples
  • Arsenic 50 samples
  • Chloride 170 samples
  • Sulfate 169 samples
  • Fluoride 314 samples
  • Lead 50 samples
  • Sodium 137 samples
  • pH 66 samples
  • Hardness 137 samples

Limited data (<15 samples) — interpret with caution

  • Uranium 9 samples

No private-well PFAS data for Washington County

We have no private well sampling data for PFAS compounds (PFOA, PFOS, PFNA, and related chemicals) in Washington County. PFAS testing for private wells requires a dedicated lab panel (~$300–$500). If you are near a military base, airport, or industrial site, consider testing proactively. Learn more about PFAS →

Public vs. Private Water in Washington County

20 Active public water systems
27,164 Residents on public water
19% 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 TX Average Source Year
Arsenic Cancer prevalence 5.7% 6.1% 2020
Arsenic Kidney disease rate 2.8% 3.3% 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 TX with at least one sample for that analyte.

Last updated: 2026-08-04

Full methodology →