Compare your result with Riverside County
Of the 1277 arsenic tests on record for Riverside County (1963–2023),
21% found none, and half were below 0.43 µg/L.
Of the 4237 chloride tests on record for Riverside County (1910–2023),
0% found none, and half were below 55 mg/L.
Of the 41 chromium (total) tests on record for Riverside County (2007–2022),
39% found none, and half were below 0.7 µg/L.
Of the 3576 fluoride tests on record for Riverside County (1947–2023),
1% found none, and half were below 550 µg/L.
Of the 2262 iron tests on record for Riverside County (1910–2023),
48% found none.
Of the 734 lead tests on record for Riverside County (1960–2023),
71% found none.
Of the 1944 manganese tests on record for Riverside County (1960–2023),
42% found none, and half were below 0.285 µg/L.
Of the 3603 nitrate tests on record for Riverside County (1910–2023),
5% found none, and half were below 1.13 mg/L.
Of the 38 pfoa tests on record for Riverside County (2020–2024),
97% found none.
Of the 38 pfos tests on record for Riverside County (2020–2024),
92% found none.
Of the 4091 sulfate tests on record for Riverside County (1910–2023),
0% found none, and half were below 78 mg/L.
Of the 41 tds tests on record for Riverside County (2007–2022),
0% found none, and half were below 390 mg/L.
Of the 612 uranium tests on record for Riverside County (2000–2023),
1% found none, and half were below 1.79 µg/L.
Public vs. Private Water in Riverside County
200
Active public water systems
2,844,604
Residents on public water
1%
Households on private wells
Public water systems in Riverside 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.
Data Sources
This report aggregates data from the following public databases:
- Water Quality Portal (WQP) — groundwater sample results for Riverside County from EPA, USGS, and state agencies. Browse WQP data →
- EPA Safe Drinking Water Information System (SDWIS) — public water system inventory used to estimate the share of residents on private wells. Browse SDWIS →
- Census ACS 5-Year Estimates — well and cistern household counts (variable DP04_0074E) used to calculate the private-well percentage for Riverside County. Census data explorer →
- USGS Aquifer Atlas — principal aquifer type underlying Riverside County, which informs which contaminants are geologically likely. USGS Aquifer Atlas →
- EPA UCMR 5 (2023–2025) — PFAS occurrence data from public water systems, used as a proxy indicator for aquifer PFAS exposure. Rows marked "municipal" in the table above come from this source. About UCMR 5 →
- EPA Toxics Release Inventory (TRI) — industrial facility chemical releases near Riverside County, used in contamination risk scoring. TRI Explorer →
- EPA Superfund NPL — National Priorities List sites in or near Riverside County, used in contamination risk scoring. Superfund site search →
- CDC PLACES — county-level health outcome prevalence (kidney disease, cancer, heart disease) correlated with detected contaminants. About CDC PLACES →
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 CA with at least one sample for that analyte.
Last updated: 2026-09-10
Full methodology →