Updated April 2026 · EPA SDWIS data
Drinking Water Trend Reports
Data-driven reports on which U.S. public water systems moved most across successive releases of the EPA Safe Drinking Water Information System. Reports surface lead service line replacement effects, the impact of EPA's 2024 PFAS rule, source-water degradation, and the systems that have improved most after investing in new treatment.
What Drives U.S. Drinking Water Trends
Two long-running shifts dominate U.S. drinking water trends right now. First, lead — the federal Lead and Copper Rule revisions and bipartisan infrastructure funding are pushing the largest lead service line replacement program in American history, with trend reports tracking which utilities are converting and which are still inventorying. Second, PFAS — EPA's April 2024 National Primary Drinking Water Regulation set the first federal MCLs for six PFAS compounds, with monitoring beginning 2027 and compliance required by 2029. That timeline means more systems will appear in PFAS-related decline reports as detection data flows into SDWIS.
Beneath those two stories, smaller-system capacity remains the biggest driver of monitoring and reporting violations. Systems serving fewer than 10,000 people — about 90% of all U.S. public water systems — concentrate the bulk of the violations in any given quarter, mostly because their compliance staffs are smaller. Trend reports filter by system size to make those patterns visible.
Worst-Graded Systems Right Now
- City of JacksonGrade F
- Newark Water DepartmentGrade F
- Tuscaloosa Water & SewerGrade F
- AtlantaGrade F
- Shreveport Water SystemGrade F
Top-Graded Systems Right Now
- Washington Suburban Sanitary CommissionGrade A
- East Bay MUDGrade A
- Dallas Water UtilityGrade A
- Charlotte WaterGrade A
- Mo American St Louis St Charles CountiesGrade A
Browse All Trend Reports
Safest Water Systems
Large water systems with the best safety records
Snapshot reports capture the current state of a slice of the EPA dataset — the worst-graded systems, the highest-violation systems, the largest detection events.
Most Water Safety Violations
Water systems with the most health-based violations
Decline reports highlight systems where violation counts and contaminant detections have moved in the wrong direction — usually a sign of aging infrastructure, treatment chemistry trouble, or a new contaminant being detected.
How Trends Are Calculated
For each system in the EPA SDWIS dataset, we compute period-over-period change in health violations, contaminant exceedances, monitoring violations, and overall Water Safety Score. We then bucket systems into "decline," "improvement," and "aggregate" reports — the latter rolling change up to the state, contaminant, or system-size level. Contaminant detection levels are joined to the corresponding EPA Maximum Contaminant Level so exceedances can be flagged automatically. The full IsWaterSafe methodology documents the calculation, edge cases, and update cadence.
Frequently Asked Questions
What is a water system trend?
A water system trend is the change over time in violations, contaminant detections, and Water Safety Score for a specific public water system, drawn from successive releases of the EPA Safe Drinking Water Information System (SDWIS). Improving systems tend to show falling violation counts after major infrastructure investments; declining systems show new violations or new contaminant detections appearing. Last refreshed April 2026.
Why are some systems suddenly worse?
Three causes dominate. First, new contaminant rules — for example, EPA's 2024 PFAS National Primary Drinking Water Regulation pushed many systems into violation when monitoring began. Second, aging infrastructure — lead service lines and aging treatment plants accumulate deferred maintenance, which surfaces as monitoring or contaminant violations. Third, source-water degradation, where upstream agriculture, industrial discharge, or saltwater intrusion changes what the utility has to treat.
Why do some systems improve?
The clearest improvement driver is lead service line replacement under the federal Lead and Copper Rule revisions. Other drivers include new treatment investments (granular activated carbon for PFAS, corrosion control for lead), source-water protection programs, and operator training that reduces monitoring violations. Trend reports identify which factor moved the score in each case.
How often is SDWIS data refreshed?
EPA refreshes the Safe Drinking Water Information System on a quarterly cycle. IsWaterSafe re-runs every trend report, system page, and ranking against the new file when each release ships. Year-over-year comparisons in the trend reports use the same quarter from each year to keep cycles consistent.
How are these reports compiled?
Each trend report takes the most recent and prior SDWIS releases, computes change in health violations, contaminant exceedances, and Water Safety Score per system, and applies the relevant filter (biggest declines, biggest improvements, aggregate state-level moves). The full IsWaterSafe methodology page documents the data joins, the violation classification, and the refresh cadence.
Sources: EPA Safe Drinking Water Information System (SDWIS), EPA National Primary Drinking Water Regulations, EPA Lead and Copper Rule revisions, EPA PFAS National Primary Drinking Water Regulation. All data is U.S. government public domain. Cite as: "IsWaterSafe, April 2026 trend reading. Data: EPA SDWIS."
Last updated 2026-04-04 · 2 trend reports · 190 systems tracked.