Water System Rankings
According to the U.S. Environmental Protection Agency Safe Drinking Water Information System (SDWIS) and the Fifth Unregulated Contaminant Monitoring Rule (UCMR5), ranked views on this page are computed directly from official public water-system records (data vintage 2026-05-15). See our methodology for how violations and PFAS detections are counted.
Each ranking pulls live from the database, refreshed when EPA publishes new SDWIS quarterly extracts or UCMR5 batches.
Worst water quality by state, at a glance
The bar to make the top 10
Where the 10th-highest state's violation rate sits among all 50 states
97.1% 10th of 50 higher than 40 of 50 states
the 50 states compared, bucketed by value
Each bar is a band; taller bars hold more states. The dashed line + filled bar mark this entry. Hover or tap any bar for its full count and share, and where it sits relative to this entry.
Source EPA Safe Drinking Water Information System (SDWIS) · 2026-05-15
Full 50-state board, methodology, and the inverse (best-quality) ranking: worst water quality by state →
Tap water quality by state
All 50 states ranked by the share of public water systems with a recorded SDWIS violation. A compliance-history rate, not a safety or taste score.
Tap water quality by state (SDWIS rates) →Best drinking water quality by state
Eligible states with the lowest share of systems carrying a recorded violation (≥25 systems). “Best” means lowest compliance-history rate, not a safety recommendation.
Best drinking water quality by state (lowest rates) →Most violations
Top 100 water systems ranked by total recorded drinking water violations across all categories tracked by EPA SDWIS.
Top 100 systems by SDWIS violations →Most common contaminants
The 50 drinking water analytes with the most EPA SDWIS violation records, ranked by total citations and systems affected.
50 most-cited SDWIS contaminants →PFAS detection by state
States ranked by share of public water systems where at least one PFAS analyte was detected during UCMR5 testing. EPA Health Advisory limit context included.
UCMR5 PFAS detection rates by state →Worst water quality by state
Superlative view: states with the highest recorded SDWIS system violation rates, paired with the lowest-rate board.
Highest SDWIS violation rates by state →PFAS detection-rate changes
States ranked by year-over-year change in PFAS detection rate among systems sampled in both 2023 and 2024 (like-for-like UCMR5 pairs).
Year-over-year PFAS detection changes →States with the most violations
All 50 states ranked by total EPA SDWIS violation counts, aggregate state totals, not a consumer safety score.
State totals for EPA SDWIS violations →Browse by US state
Every US state has its own drinking-water profile, click through for the per-state violation history, PFAS occurrence summary, and links to the public water systems serving that state.
How PlainWater rankings are compiled
Every ranking is computed directly from the EPA Safe Drinking Water Information System (SDWIS) or the EPA Fifth Unregulated Contaminant Monitoring Rule (UCMR5) dataset, never editorially curated and never blended with proprietary signals. Each ranked view links to the underlying public water system records so visitors can verify the numbers against the upstream agency.
What rankings mean (and what they do not)
A ranking is a useful navigation lens, it tells you where to start looking, but it is not a judgment about water utility quality, safety, or reputation. A high violation count typically reflects scale and reporting transparency: large utilities serving more people have more sample points and more opportunities for a single failed test to be recorded. A small rural utility with only a handful of customers can have zero recorded violations purely because the testing surface is smaller. We surface raw counts alongside the population served so visitors can sanity-check whether a number reflects systemic risk or just system size.
Why we publish these rankings
Drinking water compliance data is statutorily public under the Safe Drinking Water Act, and EPA already publishes the underlying records. PlainWater makes the rankings navigable so residents can quickly find the systems they depend on, check the recent compliance history, and click through to the official EPA Enforcement and Compliance History Online (ECHO) listing for verification. This is a long-established practice in civic data journalism; we are careful to surface the raw numbers, link to the EPA source, and avoid editorial spin.
Methodology and corrections
Most-violations ranks each public water system (PWSID) by the sum of recorded violations across all categories, Maximum Contaminant Level (MCL), Monitoring & Reporting (M&R), Public Notification, and Other. Health-based violations (the subset most directly relevant to safety) are surfaced separately. PFAS detection groups by state, divides PFAS-detected systems by total tested systems, and surfaces the detection rate. If you find a ranking that you believe is miscomputed, or a record that is misclassified, please contact us with the specific PWSID and the expected correction.
Sources
Download the SDWIS/UCMR5 state landscape snapshot cited on this page: sdwis-state-landscape.csv (same CSV as /statistics, CC0).