How our water hardness data is verified

What counts as a source

A source is the utility itself. That can be the annual water quality report or the utility's hardness page. A published FAQ counts too. Sites that collect numbers from other sites don't count. Most of them copy each other, and the numbers drift as they travel.

Each city's page names its utility and links to the source. If a link ever breaks, the utility's name and the year still show where the number came from.

How figures are recorded

Hardness is measured in parts per million (ppm) of dissolved calcium and magnesium. Some utilities use grains per gallon instead. We turn that into ppm. One grain equals 17.1 ppm.

Some utilities publish a range instead of one number. We record the middle of the range and show the full range on the city's page. Some publish one number for the whole water system. We record that number and say so on the page.

Verification and re-checks

A number enters our dataset only after we've read it on the utility's own page or in its own report. When we check a city again, its page gains a line showing the month we checked. A page without that line carries the number from our first check, with its source named. This process produces one public ranking: The hardest water cities in America.

Sometimes a re-check catches a utility in the middle of updating its own site. In August 2026, the Las Vegas Valley Water District's site gave 291 ppm in one answer and 280 in another spot on the same page. We recorded 291, the number in the utility's current main answer.

What we leave out

A number we can't confirm doesn't get published as fact. Some records carry an ESTIMATED label instead, and estimated records never appear in our rankings. Chicago shows the other problem. The documents we checked in August 2026 are image scans that no text tool can read. So Chicago's record keeps its last known number and no verification date until the city publishes something we can check.

Corrections

When a number we verified turns out wrong, we change the record and the city's page shows the new check date. The record follows whatever the utility currently publishes.