Data & Methodology — Westchester County

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

Contaminant Data — All Analytes

251 well testing events on record, covering 23 analytes. Data spans 1961 to 2023.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. NY Avg
Radon 9 1995–2018 100%
187% of limit ↑ 68% above
Manganese 164 1971–2018 79%
100% of limit ↓ 68% below
Iron 164 1971–2018 79%
34% of limit ↓ 83% below
Lead 82 1971–2018 66%
33% of limit ↑ 694% above
PFOA municipal 137 2023–2025 14%
162% of limit ~ typical
Chloride 163 1971–2018 99%
10% of limit ↓ 68% below
PFOS municipal 137 2023–2025 7%
1368% of limit ↑ 924% above
Arsenic 83 1971–2018 84%
12% of limit ↓ 35% below
PFHxS municipal 137 2023–2025 7%
68% of limit ↑ 28% above
PFNA municipal 137 2023–2025 3%
47% of limit ↓ 42% below
Fluoride 109 1971–2018 98%
4% of limit ↓ 24% below
HFPO-DA (GenX) municipal 137 2023–2025 0%
— —
Nitrate 139 1971–2018 88%
4% of limit ↓ 66% below
Nitrite 63 1971–2018 43%
0% of limit ↓ 39% below
Sulfate 163 1971–2018 100%
8% of limit ↓ 41% below
Uranium 11 1995–2018 91%
2% of limit ~ typical
E. coli 2 2008–2018 12%
— ~ typical
Fecal Coliform 2 2008–2018 12%
— ~ typical
Hardness 116 1971–2018 100%
— ↓ 47% below
PFBS municipal 137 2023–2025 5%
— ↑ 24% above
pH 164 1971–2018 100%
— ~ typical
Sodium 163 1971–2018 100%
— ↓ 75% below
Total Coliform 2 2008–2018 12%
— ~ 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 NY.

Compare your result with Westchester County

Of the 83 arsenic tests on record for Westchester County (1971–2018), 16% found none, and half were below 1 µg/L.

Of the 163 chloride tests on record for Westchester County (1971–2018), 1% found none, and half were below 23.7 mg/L.

Of the 109 fluoride tests on record for Westchester County (1971–2018), 2% found none, and half were below 170 µg/L.

Of the 164 iron tests on record for Westchester County (1971–2018), 21% found none, and half were below 27.5 µg/L.

Of the 82 lead tests on record for Westchester County (1971–2018), 34% found none, and half were below 0.87 µg/L.

Of the 164 manganese tests on record for Westchester County (1971–2018), 21% found none, and half were below 21.1 µg/L.

Of the 139 nitrate tests on record for Westchester County (1971–2018), 12% found none, and half were below 328 µg/L.

Of the 163 sulfate tests on record for Westchester County (1971–2018), 0% found none, and half were below 20.2 mg/L.

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Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • Manganese 164 samples
  • Iron 164 samples
  • Lead 82 samples
  • Chloride 163 samples
  • Arsenic 83 samples
  • Fluoride 109 samples
  • Nitrate 139 samples
  • Nitrite 63 samples
  • Sulfate 163 samples
  • Hardness 116 samples
  • pH 164 samples
  • Sodium 163 samples

Limited data (<15 samples) — interpret with caution

  • Radon 9 samples
  • Uranium 11 samples
  • E. coli 2 samples
  • Fecal Coliform 2 samples
  • Total Coliform 2 samples

No private-well PFAS data for Westchester County

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

CDC Health Outcome Correlations

Where contaminants detected in Westchester 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 Westchester County Prevalence NY Average Source Year
Lead Heart disease rate 5.7% 6.4% 2020
Arsenic Cancer prevalence 7.0% 6.7% 2020
Arsenic Kidney disease rate 2.9% 2.9% 2020

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

Last updated: 2026-08-04

Full methodology →