Lead in Tap Water by State: Which States' Systems Go Over Most
The national baseline
Of the 48,467 community water systems in EPA's records, 2,878 (5.9%) have at least one Lead and Copper Rule monitoring period with a 90th-percentile result over 15 ppb. In the latest period on file, 552 are over it now. Those totals hide a wide spread between states: in some, one system in eight or more has gone over at some point; in others it is closer to one in a hundred. This guide ranks the states on the same data the system pages use, and then explains why the ranking should be read with care before anyone concludes their state has safe or unsafe water.
States where the most systems have gone over
Ranked by the share of all community water systems that have ever been over 15 ppb, counting only states with at least 50 systems, so that a single exceedance in a tiny territory cannot top the list. "Reporting" is the share of systems with any lead result on file at all.
| State | Systems | Reporting | Ever over 15 | Over 15 now |
|---|---|---|---|---|
| Rhode Island | 93 | 83.9% | 18.3% | 6 |
| Vermont | 377 | 98.7% | 17.2% | 7 |
| Alaska | 405 | 97.3% | 13.1% | 3 |
| Massachusetts | 562 | 95.2% | 11.7% | 13 |
| Maine | 360 | 99.4% | 11.1% | 2 |
| Connecticut | 502 | 98.2% | 9.8% | 2 |
| New Hampshire | 682 | 18.2% | 9.4% | 62 |
| Pennsylvania | 1,781 | 29.0% | 8.8% | 143 |
| Illinois | 1,784 | 97.8% | 8.5% | 22 |
| South Carolina | 555 | 99.6% | 8.5% | 3 |
| New Mexico | 546 | 92.3% | 8.4% | 14 |
| New Jersey | 625 | 96.8% | 8.3% | 5 |
The states near the top share a few things. Many are in the Northeast, where much of the housing stock predates the 1986 federal ban on lead pipe and solder. Several also have a very large number of tiny systems. A single condominium, school, mobile home park or village well each counts as its own water system, and the small-system guide shows those exceed far more often than city utilities, partly because a five-home sample can be pushed over by one house.
States where the fewest have
At the other end, among states with at least 50 systems, the lowest share ever over the action level is in Hawaii (0.8%), Kentucky (1.1%), South Dakota (1.3%), Alabama (2.0%), Tennessee (2.2%), Ohio (2.5%). A low share is a real signal that sampled homes in those states have rarely tested high. It is not evidence that a given house there has no lead line, for the reason every system page repeats: the utility's 90th percentile is drawn from a handful of homes chosen to be the likeliest to have lead, and your pipe is only answered by your service line inventory entry or a test of your own tap.
Why low reporting makes a state look cleaner
The ranking above counts an exceedance only if a result was filed with EPA. Where many systems have no result on file, the share that "ever went over" is pulled down by systems that were never measured in this dataset, not by systems that measured low. The states where fewer than half of systems have any result on file are New Hampshire (18.2% reporting), Arkansas (28.7% reporting), Pennsylvania (29.0% reporting). In those states, the true rate of exceedances could be well above what the table shows, and a system page reading "no result on file" means exactly that. It does not mean the water passed. This is why the site never ranks a state as safe, and why the recommendation on a no-result page is to test.
It is also why the "ever over" column and the "over now" column can disagree. A state can have a high historical share because its systems went over years ago and corrosion control brought them down (the pattern described in over the limit before, under it now), while another state shows few exceedances only because results stopped arriving.
Where the most people are affected now
Counting systems treats a 25-person well the same as a city. Counting people served by systems over 15 ppb in their latest result gives a different order: Illinois (about 450,234 people on 22 systems), Massachusetts (about 91,260 people on 13 systems), New York (about 72,683 people on 17 systems), Pennsylvania (about 69,656 people on 143 systems), California (about 55,045 people on 30 systems). One large utility over the line can outweigh hundreds of small ones, which is why a state can look middling by share of systems and still lead by population. The population figure is what the utility reports serving, not the number of homes with lead pipes; inside an exceeding system most homes may have none.
The 2027 band, state by state
When the action level drops to 10 ppb in November 2027, systems now between 10 and 15 ppb cross the line without anything in the water changing. The states with the most systems in that band today are New York (51), Illinois (42), California (40), Washington (40), Georgia (26). The 10 ppb rule guide covers what those utilities will have to do.
How to use this for your own house
Use the state numbers as context, not as an answer. Look up your own system's page for its full period-by-period history, then check your address in the utility's service line inventory, and if anyone in the home is pregnant or a young child, test your tap through a certified lab. A state with few exceedances still has old houses with lead lines, and a state with many still has systems that have never measured lead at all. How the number on each page is produced is in how to read a lead result.
Where to go next
See the range across large systems: Aurora, IL, Metropolitan Utilities District, NE, Washington Suburban Sanitary Commission, MD.
How to Read Your Water Utility's Lead Result · The 10 ppb Lead Rule: Which Water Systems It Changes in 2027