Updated April 2026 · EPA SDWIS data
Compare Water Systems
Side-by-side comparison of Water Safety Scores, EPA health violations, and contaminant detections versus EPA Maximum Contaminant Levels for any U.S. public water system. Add as many systems as you like — every metric below is drawn from the EPA Safe Drinking Water Information System (SDWIS), supplemented with the EWG Tap Water Database for context.
Loading...
How to Read a Water System Comparison
Three metrics carry most of the signal. Health violations are formal EPA findings that a system breached a health-based standard — the most serious category, weighted 40% in the Water Safety Score. Contaminant exceedances count distinct contaminants detected above their EPA Maximum Contaminant Level over the reporting period; even a single MCL exceedance pulls the grade down sharply. Enforcement actions capture how regulators have responded — formal notices, compliance orders, and judicial actions taken against the system.
Beneath those headline numbers, the contaminant detection rows show what was actually measured. The asterisk (*) flags any reading that exceeded the EPA MCL. A reading without an asterisk is below the legal limit, but as the FAQ notes, the legal limit is not the same as a health-based goal — for several regulated contaminants, the EPA's non-enforceable health goal (MCLG) is zero. Use the contaminant pages linked from each row for the EPA MCL, MCLG, common sources, and treatment options.
What the Score Cannot Tell You
The Water Safety Score reflects what EPA SDWIS records show at the system level. It does not capture what comes out of your specific tap, which is also affected by the lead service line, household plumbing, and on-property treatment downstream of the utility's distribution point. EPA's Learn About Your Water resource explains how to read your local water utility's annual Consumer Confidence Report (CCR) — required to be published every July — for the readings specific to your address.
The score also does not assert or rule out specific health outcomes. EPA regulatory limits are designed to be protective; an MCL exceedance is a regulatory event, not a clinical diagnosis. If you have a specific health concern (an immunocompromised household member, a pregnancy, an infant on formula made with tap water, a recent lead exposure), talk to your physician and contact your local public health department for guidance.
How the Comparison Is Built
For each compared system we pull the most recent SDWIS record covering health violations, contaminant detections, monitoring violations, and enforcement history. Contaminant detection levels are joined to the EPA MCL and MCLG so exceedances can be flagged automatically. The IsWaterSafe methodology documents the exact data joins, scoring weights, and refresh cadence. Source-water classification uses the SDWIS PWS Source Type field; population served comes from the SDWIS PWS Population field.
Frequently Asked Questions
What does the Water Safety Score measure?
The IsWaterSafe Water Safety Score is a 0–100 composite drawn entirely from EPA Safe Drinking Water Information System (SDWIS) records. It weights health-based violations (40%), contaminant exceedances against EPA Maximum Contaminant Levels (30%), enforcement actions taken against the system (20%), and monitoring or reporting violations (10%). The score is then mapped to a letter grade A–F so two systems can be compared at a glance.
Are EPA Maximum Contaminant Levels (MCLs) the same as a "safe" level?
No. The EPA MCL is the legal limit set by the Safe Drinking Water Act and is the threshold a public water system must stay below to avoid a federal violation. The EPA also publishes Maximum Contaminant Level Goals (MCLGs) — non-enforceable health-based targets that for many contaminants are zero. A system can be in full legal compliance and still have detectable levels of lead, PFAS, or disinfection byproducts. Detection levels in the comparison table are reported as-is, with MCL exceedances flagged.
Can I compare more than two water systems?
Yes. The comparison tool accepts as many systems as you want to add — search by city, state, or system name to add each one. The shared metrics, the score breakdown, and any contaminants detected in any system in the comparison set are all rendered side by side. The URL updates as you add or remove systems so you can share the exact comparison.
Why do two nearby systems have very different grades?
Public water systems differ on three dimensions that move the score: source water (a system pulling from a deep protected aquifer faces fewer treatment challenges than one pulling from a surface reservoir downstream of agriculture), age and condition of the distribution network (lead service line replacement, pipe age, and treatment chemistry), and operator capacity (small systems serving fewer people often have smaller compliance staffs, which shows up in monitoring violations). Two systems in the same metro can score very differently for any of these reasons.
Where does this data come from?
Every contaminant reading, violation, and enforcement action comes from the EPA Safe Drinking Water Information System (SDWIS) federal reporting database, supplemented with EWG Tap Water Database aggregates for public communication. SDWIS is the official federal record under the Safe Drinking Water Act, refreshed quarterly by EPA. The IsWaterSafe dataset was last refreshed April 2026.
Is this medical or health advice?
No. The Water Safety Score and the underlying EPA data describe what regulators have measured at the system level — they do not diagnose, predict, or rule out any specific health outcome. Detection of a contaminant above the EPA MCL is a regulatory exceedance, not a clinical claim. If you have a specific health concern about your drinking water, talk to your physician and contact your local public health department.
Sources: EPA Safe Drinking Water Information System (SDWIS), EPA Maximum Contaminant Levels under the Safe Drinking Water Act, EWG Tap Water Database. SDWIS is U.S. government public domain. Cite as: "IsWaterSafe, April 2026 reading. Data: EPA SDWIS."
Last updated 2026-04-04 · 190 water systems tracked.