Data & Methodology — Comal County

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

Contaminant Data — All Analytes

1889 well testing events on record, covering 22 analytes. Data spans 1936 to 2018.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. TX Avg
Sulfate 671 1936–2022 96%
11% of limit ↓ 62% below
Chloride 678 1936–2022 100%
7% of limit ↓ 81% below
Iron 696 1955–2022 39%
13% of limit ↓ 91% below
Manganese 687 1956–2022 26%
4% of limit ↓ 94% below
PFOS municipal 101 2024–2025 2%
116% of limit ~ typical
PFHxS municipal 101 2024–2025 9%
37% of limit ~ typical
Fluoride 1480 1956–2022 99%
18% of limit ↓ 27% below
Nitrate 341 1936–2022 82%
16% of limit ↓ 28% below
Lead 515 1969–2022 38%
7% of limit ↓ 57% below
Arsenic 586 1971–2022 27%
4% of limit ↓ 90% below
HFPO-DA (GenX) municipal 101 2024–2025 0%
— —
Nitrite 198 1975–2022 18%
1% of limit ~ typical
PFNA municipal 101 2024–2025 0%
— —
PFOA municipal 101 2024–2025 0%
— —
Radon 17 1996–2017 100%
7% of limit ↓ 81% below
Uranium 206 1996–2022 44%
3% of limit ↓ 84% below
Total Coliform 5 1969–2018 73%
— ~ typical
Sodium 392 1955–2022 100%
— ↓ 92% below
pH 583 1955–2022 100%
— ~ typical
PFBS municipal 101 2024–2025 4%
— ↑ 123% above
Hardness 635 1936–2022 100%
— ~ typical
E. coli 5 2004–2018 69%
— ~ 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 Comal County

Of the 586 arsenic tests on record for Comal County (1971–2022), 73% found none.

Of the 678 chloride tests on record for Comal County (1936–2022), 0% found none, and half were below 17 mg/L.

Of the 1480 fluoride tests on record for Comal County (1956–2022), 1% found none, and half were below 665 µg/L.

Of the 696 iron tests on record for Comal County (1955–2022), 61% found none.

Of the 515 lead tests on record for Comal County (1969–2022), 62% found none.

Of the 687 manganese tests on record for Comal County (1956–2022), 74% found none.

Of the 341 nitrate tests on record for Comal County (1936–2022), 18% found none, and half were below 1.5 mg/L.

Of the 671 sulfate tests on record for Comal County (1936–2022), 4% found none, and half were below 25 mg/L.

Of the 206 uranium tests on record for Comal County (1996–2022), 56% found none.

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Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • Sulfate 671 samples
  • Chloride 678 samples
  • Iron 696 samples
  • Manganese 687 samples
  • Fluoride 1480 samples
  • Nitrate 341 samples
  • Lead 515 samples
  • Arsenic 586 samples
  • Nitrite 198 samples
  • Radon 17 samples
  • Uranium 206 samples
  • Sodium 392 samples
  • pH 583 samples
  • Hardness 635 samples

Limited data (<15 samples) — interpret with caution

  • Total Coliform 5 samples
  • E. coli 5 samples

No private-well PFAS data for Comal County

We have no private well sampling data for PFAS compounds (PFOA, PFOS, PFNA, and related chemicals) in Comal 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 Comal County

96 Active public water systems
233,262 Residents on public water
4% Households on private wells

Public water systems in Comal 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 Comal 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 Comal County Prevalence TX Average Source Year
Arsenic Cancer prevalence 7.1% 6.1% 2020
Arsenic Kidney disease rate 3.0% 3.3% 2020
Lead Heart disease rate 5.3% 7.4% 2020

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