How to Read Your Water Utility's Lead Result

One number per monitoring period

Under the Lead and Copper Rule a utility samples first-draw tap water from a set of homes, sorts the results, and reports the value 90% of them came in at or under - the 90th percentile. If that is above 15 ppb, more than one sampled home in ten was over, and the system has "exceeded the action level". That is the number on every system page here; 44,481 of 48,467 community water systems have at least one on file with EPA.

The sampled homes are chosen to be the worst

Utilities do not sample at random. The rule tells them to pick homes most likely to have lead - homes with lead service lines first, then homes with lead solder from the early 1980s. So the 90th percentile is already a high-end figure for the system. It is still not your tap: a home with a lead line in a system reporting 2 ppb can measure far more, and a home with copper pipes in a system over 15 can measure nothing.

"Reported as 0" is not "lead-free"

18,000 systems - 40.5% of those with a result - report their latest 90th percentile as 0. That means the sampled homes came in under the lab's detection limit, not that there is no lead anywhere. EPA's health goal for lead is zero precisely because no level is known to be safe, and a zero result says nothing about whether a lead service line runs to any particular house.

Systems with nothing on file

3,986 systems have no lead result in EPA's database at all - usually very small systems, or states that report late. Their pages say "no result on file" and recommend a tap test, because there is nothing else to go on.

Why some periods end in the future

Small systems that keep testing low are allowed to sample less often - every three years, sometimes nine. EPA records the whole monitoring window, so a result can carry an end date a year or two ahead. The result is real; the window just has not closed yet.

How the recommendation is set

Over 15 ppb now: filter, then test. Over 10 ppb, or over 15 at any time before: test your tap. Detected but low: test if the house was built before 1986 or a pregnant person or young child lives there. Reported as 0: look up your address in the service line inventory. These tiers are our rules over EPA's thresholds; every page shows the raw ppb next to them.

Where to go next

See the range across large systems: Aurora, IL, Metropolitan Utilities District, NE, Washington Suburban Sanitary Commission, MD.

The 10 ppb Lead Rule: Which Water Systems It Changes in 2027 · Why Small Water Systems Go Over the Lead Limit More Often