Why Small Water Systems Go Over the Lead Limit More Often
Exceedances by size
Grouping every community water system by the population it serves, the share with at least one period over 15 ppb, and the share over it in the latest period:
| People served | Systems | Ever over 15 | Over 15 now |
|---|---|---|---|
| 500 people or fewer | 25,967 | 7.4% | 1.8% |
| 501-3,300 | 12,996 | 4.8% | 0.9% |
| 3,301-10,000 | 4,931 | 3.7% | 0.4% |
| 10,001-100,000 | 4,087 | 3.4% | 0.4% |
| over 100,000 | 486 | 4.5% | 0.4% |
Why size matters
Systems serving 500 people or fewer are over 15 ppb right now at 1.8%, against 0.4% for systems serving over 100,000. Part of it is real: small systems - trailer parks, rural districts, a single subdivision well - rarely have staff to run corrosion control, the treatment that keeps lead from leaching out of pipes. Part of it is arithmetic: a small system samples as few as five homes, so one high home can put the 90th percentile over the line. Either way, the result is from homes on that system.
Groundwater and surface water
6.6% of groundwater systems have gone over at some point, against 5.9% of surface-water systems. Most very small systems run on wells, so this mostly repeats the size pattern; well water can also be more corrosive when it is untreated.
Big systems are not off the hook
A big city's low 90th percentile is drawn from tens of thousands of homes, and it can hide streets of older houses with lead lines. 3.4% of systems serving 10,001-100,000 people have gone over at some point. On a large system, your own service line record matters more than the system-wide number.
Where to go next
See the range across large systems: Aurora, IL, Metropolitan Utilities District, NE, Washington Suburban Sanitary Commission, MD.
Over the Lead Limit Before, Under It Now: What That Means · How to Read Your Water Utility's Lead Result