Water data studies
We assemble the public certification listings (NSF/WQA/IAPMO) and EPA drinking-water data (UCMR5, SDWIS, the Lead & Copper Rule) that no one else has joined in one place — then rank it. Every figure is sourced and public domain, free to republish with attribution. Updated July 2026, covering 21,807 U.S. public water systems.
PFAS 'Forever Chemicals' in U.S. Tap Water
EPA's UCMR5 program found PFOA or PFOS above the 2024 federal limit of 4 parts per trillion in 1,721 public water systems — serving about 81 million people.
The True Cost of a Water Filter, per Gallon
The cheapest filter to buy is often the most expensive water to drink. We calculated the real cost per gallon — price ÷ certified capacity — for 1,010 certified filters. Pitcher filters cost about 31× more per gallon than under-sink filters.
Disinfection Byproducts (TTHM & HAA5) in U.S. Tap Water
Chlorine keeps tap water free of deadly germs — but it also reacts with natural matter to form “disinfection byproducts” linked to cancer risk over long exposure. We found 2,551 systems over the federal limit, serving about 20 million people.
Most Water Filters Are Certified for Taste — Not Health
A certification seal doesn’t mean a filter removes anything harmful. Of 5,682 certified filters, 43% carry only NSF/ANSI 42 — an aesthetic standard for taste and odor — with no health-contaminant certification.
EPA Drinking-Water Violations, by State and System
13,323 public water systems in our data carry at least one EPA drinking-water violation on record since 2016 — 61,474 violations in total.
Lead in U.S. Tap Water, by State and System
723 public water systems reported a 90th-percentile lead sample above the EPA’s 15 ppb action level. There is no safe level of lead in drinking water.
Journalists & researchers: all figures are free to republish with attribution (CC-BY 4.0) and a link. Machine-readable data is at dataset.json. Questions or a custom cut? See our methodology.