YourWaterReport.com aggregates groundwater quality data from public federal and state databases to help private well owners understand what contaminants may be present in their area. This page documents exactly where our data comes from, how it is processed, and where its limitations lie.
Data sources
All contaminant occurrence data displayed on this site comes from publicly available government databases. We do not generate, sample, or certify any water quality data. Our role is aggregation, geographic linking, and presentation.
Water Quality Portal (WQP)
The Water Quality Portal (waterqualitydata.us) is a cooperative service operated by the USGS, EPA, and USDA that integrates water quality data from over 400 federal, state, tribal, and local agencies. It contains hundreds of millions of records spanning decades of groundwater monitoring. WQP is our primary data source for groundwater analyte measurements.
We query WQP for groundwater records by county FIPS code and analyte name. Results include sample date, sample depth, monitoring location coordinates, analytical method, and measured value.
USGS National Water Information System (NWIS)
USGS NWIS provides groundwater level data, well depth and construction data, and aquifer information for monitoring wells across the country. We use NWIS to supplement WQP records and to provide aquifer-type context for county-level patterns.
U.S. Census Bureau (American Community Survey)
We use ACS 5-year estimates for county-level housing age data — specifically the percentage of housing units built before 1986, which serves as a proxy for lead exposure risk from pre-1986 plumbing (lead solder was banned in 1986).
EPA ECHO (Enforcement and Compliance History Online)
For county pages that include information on nearby regulated facilities or public water system compliance history, we query EPA's ECHO database. This is supplementary to our primary WQP-based well water data.
Geographic aggregation
All data is aggregated at the county level using FIPS codes (5-digit Federal Information Processing Standard county identifiers). Geographic assignments are made by associating monitoring location coordinates with county boundaries using Census TIGER shapefiles.
County-level statistics are computed from all groundwater records in WQP for that county, filtered to the relevant analyte and sample type. We report:
- Median concentration — the 50th percentile of all measurements in the county dataset
- 90th percentile concentration — useful for identifying the upper range of exposure within a county
- Detection frequency — percentage of samples with measured values above the method detection limit
- Sample count — the number of individual measurements underlying the statistics
- Date range — the span of sample dates included
Analytes covered
We currently aggregate and display county-level data for the following parameters:
| Analyte | WQP Characteristic Name | Units |
|---|---|---|
| Arsenic | Arsenic | µg/L |
| Nitrate | Nitrate | mg/L as N |
| Uranium | Uranium | µg/L |
| Radium-226 | Radium-226 | pCi/L |
| Radium-228 | Radium-228 | pCi/L |
| Fluoride | Fluoride | mg/L |
| Iron | Iron | µg/L |
| Manganese | Manganese | µg/L |
| pH | pH | standard units |
| Hardness | Hardness, Ca, Mg | mg/L as CaCO₃ |
| Turbidity | Turbidity | NTU |
Note: PFAS, lead, E. coli, chromium, radon, and mercury are important private well water contaminants but are not currently included in county-level aggregates due to data sparsity or sampling methodology constraints. We display contextual information about these contaminants on county pages where documented contamination exists in public records.
Data limitations
Our data is only as comprehensive as the underlying public monitoring records. Important limitations to understand:
- Monitoring wells ≠ private wells. Most WQP groundwater records come from municipal, research, or regulatory monitoring wells. These may not represent the specific aquifer your private well draws from.
- Geographic variation within counties. County-level statistics mask substantial within-county variation. Two wells in the same county can have very different water quality depending on well depth, aquifer type, and local geology. County data should be interpreted as a rough indicator, not a prediction for any specific well.
- Historical data. Some WQP records are decades old. Water quality can change over time due to land use changes, well aging, and groundwater level fluctuations.
- Not all wells are sampled. Private wells are not required to be reported to any public database. WQP records represent wells that were sampled for regulatory, research, or remediation purposes — not a random sample of all private wells.
- Detection limits vary by method and laboratory. A "not detected" result does not mean a contaminant is absent — it means the concentration was below the method's detection threshold, which varies.
Update schedule
County-level aggregates are refreshed quarterly from WQP via automated API queries. The most recent update date is displayed on each county page. Housing age data (Census ACS) is updated on the ACS release schedule (approximately annually for 5-year estimates).
Contaminant content standards
All health and regulatory information on contaminant guide pages is sourced from:
- U.S. Environmental Protection Agency (EPA) drinking water standards and health advisories
- IARC (International Agency for Research on Cancer) carcinogen classifications
- Peer-reviewed literature cited at the bottom of each contaminant guide page
- WHO drinking water quality guidelines
We do not accept payment to modify or favor any contaminant risk assessment. Our content does not reflect the interests of the water treatment industry.
Questions or corrections
If you find an error in our data or methodology, please use our contact page to get in touch.