Press and citation guide

CheckYourWater is a free, open-source public service tool that grades every public water system in the United States for PFAS contamination using official EPA testing data. Anyone can search by zip code to find the grade for their own water.

The data comes from the EPA Unregulated Contaminant Monitoring Rule, fifth cycle (UCMR 5), which tested over 10,000 public water systems for 29 PFAS compounds between 2023 and 2025. We assign letter grades from A through F based on detected levels relative to the EPA enforceable limits finalized in April 2024.

CheckYourWater is not affiliated with the EPA, any other government agency, any water utility, or any chemical manufacturer. The project receives no industry funding.

For reporters working statewide stories we also publish per-state pages aggregating EPA UCMR 5 testing results, a ranked list of the worst-affected water systems in each state, and a summary of that state’s PFAS regulatory response.

Every grade is calculated from a single data source: the EPA UCMR 5 occurrence data file. For each water system we identify the worst single compound result across the testing period and compare it to the federal Maximum Contaminant Level (MCL) for that compound.

• A: No PFAS compounds detected above the Minimum Reporting Level.
• B: PFAS detected, all results below 50% of the federal MCL.
• C: Worst compound between 50% and 100% of the federal MCL.
• D: At least one compound above the federal MCL, up to five times the limit.
• F: At least one compound more than five times the federal MCL.

Read the full methodology, including known limitations →