Data & Methodology — Philadelphia County

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

Contaminant Data — All Analytes

1297 well testing events on record, covering 18 analytes. Data spans 1912 to 2023.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. PA Avg
Iron 1073 1929–1986 99%
367% of limit ↓ 37% below
PFOA municipal 28 2024–2025 86%
145% of limit ↑ 56% above
Manganese 210 1945–1986 99%
500% of limit ~ typical
PFOS municipal 28 2024–2025 79%
89% of limit ↓ 30% below
Arsenic 95 1979–1986 35%
50% of limit ↑ 71% above
Nitrate 1070 1929–1986 99%
1% of limit ↓ 92% below
Lead 94 1945–1986 34%
0% of limit ↓ 100% below
Sulfate 1198 1929–1986 100%
17% of limit ~ typical
Chloride 1212 1929–1986 100%
13% of limit ↑ 21% above
Nitrite 99 1943–1986 83%
1% of limit ↓ 33% below
Fluoride 271 1945–1986 100%
5% of limit ~ typical
HFPO-DA (GenX) municipal 28 2024–2025 0%
— —
PFHxS municipal 12 2024 0%
— —
PFNA municipal 12 2024 17%
45% of limit ↓ 33% below
Hardness 1192 1929–1986 100%
— ~ typical
PFBS municipal 28 2024–2025 82%
— ~ typical
pH 1243 1943–2001 100%
— ~ typical
Sodium 223 1929–1986 100%
— ↑ 112% above

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 PA.

Compare your result with Philadelphia County

Of the 95 arsenic tests on record for Philadelphia County (1979–1986), 65% found none.

Of the 1212 chloride tests on record for Philadelphia County (1929–1986), 0% found none, and half were below 32.2 mg/L.

Of the 271 fluoride tests on record for Philadelphia County (1945–1986), 0% found none, and half were below 200 µg/L.

Of the 1073 iron tests on record for Philadelphia County (1929–1986), 1% found none, and half were below 1.05 mg/L.

Of the 94 lead tests on record for Philadelphia County (1945–1986), 66% found none.

Of the 210 manganese tests on record for Philadelphia County (1945–1986), 1% found none, and half were below 250 µg/L.

Of the 1070 nitrate tests on record for Philadelphia County (1929–1986), 1% found none, and half were below 140 µg/L.

Of the 1198 sulfate tests on record for Philadelphia County (1929–1986), 0% found none, and half were below 42 mg/L.

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Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • Iron 1073 samples
  • PFOA 28 samples
  • Manganese 210 samples
  • PFOS 28 samples
  • Arsenic 95 samples
  • Nitrate 1070 samples
  • Lead 94 samples
  • Sulfate 1198 samples
  • Chloride 1212 samples
  • Nitrite 99 samples
  • Fluoride 271 samples
  • HFPO-DA (GenX) 28 samples
  • Hardness 1192 samples
  • PFBS 28 samples
  • pH 1243 samples
  • Sodium 223 samples

Public vs. Private Water in Philadelphia County

6 Active public water systems
1,601,175 Residents on public water

Public water systems in Philadelphia 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 Philadelphia 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 Philadelphia County Prevalence PA Average Source Year
Arsenic Cancer prevalence 5.4% 7.0% 2020
Lead Heart disease rate 6.4% 7.2% 2020
Arsenic Kidney disease rate 3.3% 3.0% 2020

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

Last updated: 2026-08-04

Full methodology →