Data & Methodology — Williams County

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

Contaminant Data — All Analytes

169 well testing events on record, covering 22 analytes. Data spans 1965 to 2024.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. OH Avg
Iron 160 1972–2016 98%
383% of limit ~ typical
Manganese 155 1972–2016 96%
32% of limit ↓ 82% below
Sulfate 103 1972–2016 97%
11% of limit ↓ 74% below
Arsenic 79 1985–2016 82%
0% of limit ↓ 100% below
Chloride 159 1972–2016 100%
5% of limit ↓ 66% below
Lead 83 1972–2016 65%
0% of limit ↓ 100% below
Fluoride 137 1972–2016 100%
25% of limit ↑ 144% above
HFPO-DA (GenX) municipal 4 2023–2024 0%
— —
Nitrate 49 1972–2016 33%
0% of limit ↓ 91% below
Nitrite 99 1974–2016 15%
1% of limit ↑ 73% above
PFHxS municipal 4 2023–2024 0%
— —
PFNA municipal 4 2023–2024 0%
— —
PFOA municipal 4 2023–2024 0%
— —
PFOS municipal 4 2023–2024 0%
— —
Radon 6 1998–2002 100%
7% of limit ↓ 68% below
Uranium 13 2002–2016 100%
1% of limit ↓ 60% below
pH 157 1972–2016 100%
— ~ typical
Sodium 160 1972–2016 100%
— ~ typical
Total Coliform 4 2007–2016 10%
— ~ typical
E. coli 4 2007–2016 10%
— ~ typical
Hardness 143 1972–2016 100%
— ↓ 22% below
PFBS municipal 4 2023–2024 0%
— —

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 OH.

Compare your result with Williams County

Of the 79 arsenic tests on record for Williams County (1985–2016), 18% found none.

Of the 159 chloride tests on record for Williams County (1972–2016), 0% found none, and half were below 13 mg/L.

Of the 137 fluoride tests on record for Williams County (1972–2016), 0% found none, and half were below 1 mg/L.

Of the 160 iron tests on record for Williams County (1972–2016), 2% found none, and half were below 1.15 mg/L.

Of the 83 lead tests on record for Williams County (1972–2016), 35% found none.

Of the 155 manganese tests on record for Williams County (1972–2016), 4% found none, and half were below 15 µg/L.

Of the 49 nitrate tests on record for Williams County (1972–2016), 67% found none.

Of the 103 sulfate tests on record for Williams County (1972–2016), 3% found none, and half were below 28 mg/L.

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Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • Iron 160 samples
  • Manganese 155 samples
  • Sulfate 103 samples
  • Arsenic 79 samples
  • Chloride 159 samples
  • Lead 83 samples
  • Fluoride 137 samples
  • Nitrate 49 samples
  • Nitrite 99 samples
  • pH 157 samples
  • Sodium 160 samples
  • Hardness 143 samples

Limited data (<15 samples) — interpret with caution

  • Radon 6 samples
  • Uranium 13 samples
  • Total Coliform 4 samples
  • E. coli 4 samples

No private-well PFAS data for Williams County

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

44 Active public water systems
27,059 Residents on public water
41% Households on private wells

Public water systems in Williams 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 Williams 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 Williams County Prevalence OH Average Source Year
Arsenic Kidney disease rate 3.3% 3.1% 2020
Arsenic Cancer prevalence 7.9% 6.8% 2020
Lead Heart disease rate 6.5% 7.6% 2020

Source: CDC PLACES county-level estimates. Raw data: Download Williams 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 OH with at least one sample for that analyte.

Last updated: 2026-08-04

Full methodology →