Sources

Everything on Tapped Out comes from public records plus our own calculations. Figures are estimates, not 100% accurate or guaranteed.

Public datasets

• EPA SDWIS (water systems, violations, lead and copper results). Public domain U.S. government data.
• EPA UCMR 5 (PFAS and lithium sampling). Public domain.
• EPA ECHO (linked system records).
• U.S. Census Bureau population estimates. Public domain.
• County hardness estimates: Hard Water Map (CC BY 4.0, attributed on each page), derived from the USGS/EPA Water Quality Portal. These describe untreated local water, not your tap, and are labeled low confidence.

Utility water quality reports

Where a utility publishes hardness in its annual Consumer Confidence Report, we record the figure, units and year, and link to the report. We don't copy report text, tables or images. Facts like a hardness value are cited, not reproduced. Figures we couldn't verify against the utility's own report are marked “Unverified source”.

Calculator references

Calculators cite their references (EPA, CDC, USGS, NSF and university extension) on each page. See how we calculate.

We're independent and not affiliated with the EPA, the Census Bureau, any utility or any data provider listed here.

Last updated October 21, 2026.