Sources & Data

HardWaterHQ is built on primary sources. Here's exactly where each data point comes from.

Water hardness (GPG / ppm)

• Municipal water-quality reports — each city's published Consumer Confidence Report (CCR) or Annual Water Quality Report. This is the primary source of truth for hardness.
• USGS Water Science School — for the standard hardness classification ranges.

Contaminant data

• EWG Tap Water Database — contaminant detections, levels above health or legal guidance, and utility-level breakdowns.
• U.S. EPA — Maximum Contaminant Levels (MCLs) and health advisory thresholds.
• Health Canada — Maximum Acceptable Concentrations (MACs) for Canadian cities.

Water source & utility

• Each city page names the serving utility and its water source (river, reservoir, aquifer, or system of sources). These are verified against the utility's own published materials website-by-website, not taken from a single third-party aggregator.

Licensing

Aggregate hardness figures from TapWaterData were used under its CC BY 4.0 license as a starting index; individual city values are verified against primary utility reports before publication. Original analysis, editorial content, and the cost/contaminant modeling on HardWaterHQ are © 2026 Gravison Group.

Found an error or a stale figure? Let us know and we'll verify and correct it.