Every reading on a city page comes from one of three places: national testing by the U.S. Environmental Protection Agency (EPA), EPA’s federal drinking water database, or the water utility’s own published data, usually its annual water quality report. Prices, wages and study findings on other pages come from the sources cited next to them. We cite the source where the number appears, and we never type a reading into a page by hand. Each one is read from a data file, and the site’s build fails if a page and its data disagree.
The water system is the unit
Water is delivered by water systems, not by towns, and their boundaries rarely match city limits. Many suburbs buy their water from the core city’s utility. So each city page describes one water system, identified by its EPA system ID, and lists the other systems that buy water from it.
PFAS, lithium and disinfectant: EPA UCMR 5
EPA’s fifth Unregulated Contaminant Monitoring Rule sampled drinking water across the country from 2023 to 2025 for 29 PFAS (“forever chemicals”) and lithium. We use the final national file (posted 2026-10-15). For each system we report the number of samples, how many found the chemical, and the highest result. A result below EPA’s reporting level counts as not detected.
These are samples, not compliance results. Under EPA’s PFAS rule (89 FR 32532), compliance is judged on a running annual average starting in 2029. Lithium has no legal limit; we compare it with EPA’s health reference level of 10 micrograms per liter (µg/L) the way EPA does, at one significant digit.
The same file records the disinfectant each sampling point uses. A point counts as chloramine if the utility reported any chloramine there. Where the utility’s own report says otherwise, the utility’s statement wins.
Violations and who buys from whom: EPA SDWIS
EPA’s Safe Drinking Water Information System, through its ECHO download (2026Q3 file), gives each system’s population, its source water, its violations and the systems that buy water from it. We count health-based violations in the five years through September 2026, once per violation.
Hardness: the utility’s own report
No reliable national hardness file exists. The one most often repeated online mixes county-level estimates with utility data and assigns some towns to the wrong utility, so we don’t use it. Instead we read hardness from each utility’s latest annual water quality report and record the report year, the page and the date we read it. Where a utility publishes a range or figures for several plants, we show the range. Classes follow the U.S. Geological Survey (USGS) hardness scale.
What we don’t do
- We don’t rate or rank products or companies. City pages show where a system’s readings fall among the systems we cover (for example, "3rd hardest"), which is a comparison of EPA and utility numbers, not a grade.
- We don’t call water "safe" or "unsafe." We say whether a reading is above or under EPA’s level, and what kind of level it is.
- We don’t take payment for coverage. How the site makes money is on our disclosure page.
Corrections
If a number on this site disagrees with your utility’s latest report, tell us at help@thewatermonitor.com with a link to the report. We fix confirmed errors and note the date on the page.