Top 25 worst states for tap water quality
Same methodology as our state rankings table: each state is ordered by the % of tracked citieswith UCMR5 PFAS over an EPA limit or an MCL violation flag. Letter grades use that percentage (A = 0–10% at risk, … F = 75%+). "Worst city" links use the lowest Water Safety Score in that state.
Note: Rankings reflect WaterCheckup city guides, not every public water system in the state. For a composite city score list see worst cities by safety score.
Alabama is home to one of the most PFAS-contaminated water systems in the Southeast near Anniston — where Monsanto manufactured PCBs and PFAS for decades. The Anniston Army Depot also used AFFF. 81 systems across the state exceed federal PFAS limits. Alabama has some of the weakest state-level water quality enforcement in the US.
Colorado's PFAS contamination centers on Buckley Space Force Base and Peterson Air Force Base in the Colorado Springs area. PFHxS was detected at 28 ppt — 3× the EPA limit — in affected systems. Denver Water's use of chloramine produces DBPs not removed by standard filters, and the city has pre-1986 lead infrastructure concerns.
Connecticut has 36 systems above EPA PFAS limits, many tied to military installations including Groton Naval Submarine Base. The state has compact geography with high industrial density and aging infrastructure. Chloramine DBPs are a secondary concern in several larger public water systems.
Illinois has 35 systems above PFAS limits and Chicago — with 150,000+ lead service lines — represents one of the largest single lead infrastructure challenges in the US. Chicago uses chloramine, which produces NDMA and DBPs not addressed by standard carbon filters. Several downstate systems have PFAS from industrial sources.
Indiana has 23 systems above PFAS limits with PFHxS at 26 ppt near Grissom Air Reserve Base. Camp Atterbury and other military installations have contributed AFFF contamination. Indianapolis has lead concerns in older neighborhoods, and several smaller public water systems have struggled with monitoring compliance.
Kentucky has 36 systems above PFAS limits with contamination traced to military sites and industrial facilities. Louisville draws from the Ohio River, which carries industrial contamination from upstream states. The state has documented challenges with aging rural infrastructure and monitoring compliance.
Mississippi has significant infrastructure challenges compounded by the Jackson water crisis — the city faced the longest municipal boil water advisory in US history in 2022–2023. Lead contamination, aging pipes, and treatment failures have left Jackson residents without reliable safe water for years. Rural systems across the state face chronic monitoring violations.
Nevada's primary water problem is geological — Las Vegas and Henderson draw from the Colorado River and Lake Mead, which delivers water with extremely high TDS (total dissolved solids) and hardness. This hard water requires aggressive treatment that produces elevated disinfection byproducts. Nevada also has natural arsenic in groundwater serving several smaller communities.
New Jersey has some of the strictest state PFAS standards in the country — stricter than EPA — yet still has 158 systems above federal limits. The industrial density of the state, legacy Superfund sites, and military installations have left widespread groundwater contamination. Newark recently completed lead pipe replacement after a high-profile crisis.
South Carolina has North Charleston as one of the worst single-system PFAS readings nationally — HFPO-DA (GenX) at 140 ppt, 14× the EPA limit — traced to Charleston Air Force Base AFFF use. The state has 69 systems above EPA limits, making it one of the most contaminated per capita in the Southeast.
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