Data & Methodology — Hays County

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

Contaminant Data — All Analytes

1984 well testing events on record, covering 22 analytes. Data spans 1937 to 2025.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. TX Avg
Sulfate 730 1937–2022 100%
12% of limit ↓ 58% below
Chloride 729 1937–2022 100%
6% of limit ↓ 82% below
Iron 925 1939–2022 47%
20% of limit ↓ 87% below
Fluoride 1554 1938–2022 99%
12% of limit ↓ 48% below
Manganese 817 1939–2022 39%
5% of limit ↓ 93% below
Arsenic 780 1976–2022 32%
4% of limit ↓ 90% below
Nitrate 607 1937–2022 82%
13% of limit ↓ 42% below
Lead 700 1968–2022 26%
2% of limit ↓ 88% below
HFPO-DA (GenX) municipal 101 2023–2025 0%
— —
Nitrite 447 1976–2022 15%
1% of limit ~ typical
PFHxS municipal 101 2023–2025 3%
30% of limit ↓ 32% below
PFNA municipal 101 2023–2025 0%
— —
PFOA municipal 101 2023–2025 0%
— —
PFOS municipal 101 2023–2025 0%
— —
Radon 9 1996–2017 100%
6% of limit ↓ 82% below
Uranium 383 1980–2022 42%
3% of limit ↓ 83% below
E. coli 5 2006–2018 11%
— ~ typical
Hardness 700 1937–2022 100%
— ↑ 32% above
PFBS municipal 101 2023–2025 2%
— ↑ 28% above
pH 768 1937–2024 100%
— ~ typical
Sodium 470 1959–2022 100%
— ↓ 94% below
Total Coliform 5 1968–2018 55%
— ~ 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 Hays County

Of the 780 arsenic tests on record for Hays County (1976–2022), 68% found none.

Of the 729 chloride tests on record for Hays County (1937–2022), 0% found none, and half were below 16 mg/L.

Of the 1554 fluoride tests on record for Hays County (1938–2022), 1% found none, and half were below 464 µg/L.

Of the 925 iron tests on record for Hays County (1939–2022), 53% found none.

Of the 700 lead tests on record for Hays County (1968–2022), 74% found none.

Of the 817 manganese tests on record for Hays County (1939–2022), 61% found none.

Of the 607 nitrate tests on record for Hays County (1937–2022), 18% found none, and half were below 1.17 mg/L.

Of the 730 sulfate tests on record for Hays County (1937–2022), 0% found none, and half were below 30 mg/L.

Of the 383 uranium tests on record for Hays County (1980–2022), 58% found none.

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Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • Sulfate 730 samples
  • Chloride 729 samples
  • Iron 925 samples
  • Fluoride 1554 samples
  • Manganese 817 samples
  • Arsenic 780 samples
  • Nitrate 607 samples
  • Lead 700 samples
  • Nitrite 447 samples
  • Uranium 383 samples
  • Hardness 700 samples
  • pH 768 samples
  • Sodium 470 samples

Limited data (<15 samples) — interpret with caution

  • Radon 9 samples
  • E. coli 5 samples
  • Total Coliform 5 samples

No private-well PFAS data for Hays County

We have no private well sampling data for PFAS compounds (PFOA, PFOS, PFNA, and related chemicals) in Hays County. PFAS has been detected in local public water systems (UCMR 5 data) — indicated by the "municipal" badge in the table above — but this does not directly indicate private well contamination. 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 Hays County

122 Active public water systems
307,153 Residents on public water
8% Households on private wells

Public water systems in Hays 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 Hays 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 Hays County Prevalence TX Average Source Year
Arsenic Cancer prevalence 5.0% 6.1% 2020
Arsenic Kidney disease rate 2.5% 3.3% 2020
Lead Heart disease rate 5.7% 7.4% 2020

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