Data & Methodology — Harris County

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

Contaminant Data — All Analytes

3702 well testing events on record, covering 20 analytes. Data spans 1935 to 2025.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. TX Avg
Radon 79 2002–2016 100%
157% of limit ↑ 335% above
Iron 1522 1917–2021 85%
33% of limit ↓ 78% below
Manganese 947 1948–2021 81%
13% of limit ↓ 80% below
PFOS municipal 1319 2023–2025 4%
118% of limit ~ typical
Arsenic 661 1963–2021 70%
24% of limit ↓ 37% below
Nitrate 216 1979–2015 73%
2% of limit ↓ 91% below
Uranium 371 1984–2021 82%
5% of limit ↓ 65% below
Chloride 1848 1935–2016 100%
18% of limit ↓ 50% below
Fluoride 1567 1929–2021 98%
12% of limit ↓ 51% below
Sulfate 628 1935–2016 98%
4% of limit ↓ 86% below
PFHxS municipal 1319 2023–2025 7%
35% of limit ↓ 21% below
HFPO-DA (GenX) municipal 1319 2023–2025 0%
— —
Lead 458 1963–2021 22%
1% of limit ↓ 94% below
Nitrite 139 1982–2015 14%
0% of limit ↓ 51% below
PFNA municipal 1319 2023–2025 0%
— —
PFOA municipal 1319 2023–2025 0%
100% of limit ~ typical
Hardness 390 1935–2016 100%
— ↓ 37% below
PFBS municipal 1319 2023–2025 9%
— ~ typical
pH 1851 1957–2016 100%
— ~ typical
Sodium 387 1957–2016 100%
— ↓ 59% below

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 Harris County

Of the 661 arsenic tests on record for Harris County (1963–2021), 30% found none, and half were below 1.6 µg/L.

Of the 1848 chloride tests on record for Harris County (1935–2016), 0% found none, and half were below 45 mg/L.

Of the 1567 fluoride tests on record for Harris County (1929–2021), 2% found none, and half were below 430 µg/L.

Of the 1522 iron tests on record for Harris County (1917–2021), 15% found none, and half were below 100 µg/L.

Of the 458 lead tests on record for Harris County (1963–2021), 78% found none.

Of the 947 manganese tests on record for Harris County (1948–2021), 19% found none, and half were below 1.59 µg/L.

Of the 216 nitrate tests on record for Harris County (1979–2015), 27% found none, and half were below 160 µg/L.

Of the 628 sulfate tests on record for Harris County (1935–2016), 2% found none, and half were below 9.99 mg/L.

Of the 371 uranium tests on record for Harris County (1984–2021), 18% found none, and half were below 1.02 µg/L.

Have a number from your lab? Enter it to see where it falls. Nothing is sent anywhere.

Want the full picture for your well? Check all your results.

Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • Radon 79 samples
  • Iron 1522 samples
  • Manganese 947 samples
  • Arsenic 661 samples
  • Nitrate 216 samples
  • Uranium 371 samples
  • Chloride 1848 samples
  • Fluoride 1567 samples
  • Sulfate 628 samples
  • Lead 458 samples
  • Nitrite 139 samples
  • Hardness 390 samples
  • pH 1851 samples
  • Sodium 387 samples

No private-well PFAS data for Harris County

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

1298 Active public water systems
6,053,562 Residents on public water
1% Households on private wells

Public water systems in Harris 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 Harris 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 Harris County Prevalence TX Average Source Year
Arsenic Cancer prevalence 5.1% 6.1% 2020
Arsenic Kidney disease rate 3.0% 3.3% 2020

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