Water Hardness Lookup
Enter your ZIP to get your area's water hardness in grains per gallon, sourced from USGS and water authority data, plus a softener recommendation.
Water hardness scale
| Category | GPG | mg/L (PPM) | What you notice |
|---|---|---|---|
| Soft | 0 – 3 | 0 – 50 | No scale; soaps lather easily |
| Slightly hard | 3.5 – 7 | 60 – 120 | Minor spots on glass; acceptable for most appliances |
| Moderately hard | 7 – 10.5 | 120 – 180 | Visible scale on fixtures; water heater efficiency drops ~15% |
| Hard | 10.5 – 14 | 180 – 240 | Heavy scale; water heater life shortened; softener recommended |
| Very hard | > 14 | > 240 | Rapid appliance damage; softener strongly recommended |
What water hardness actually costs you
Hard water (above 7 GPG) deposits calcium carbonate scale inside water heaters, reducing thermal efficiency. A University of New Mexico study found that a standard tank water heater loses roughly 1.5% efficiency per GPG of hardness over its lifespan. At 18 GPG (Kansas, Nebraska, Arizona), that's 27% efficiency loss — equivalent to paying for 1.27 water heaters' worth of energy.
How we determine your hardness
- ZIP to state. Your ZIP's first 3 digits map to a state via USPS sectional center prefixes. The calculator uses the state median — not an exact well measurement for your address.
- USGS source data. State medians are derived from the USGS National Water-Quality Assessment Program and published water utility Consumer Confidence Reports. High-plains states (KS, NE, SD, AZ, ND) typically exceed 17 GPG; New England states (ME, VT, NH, MA) average under 4 GPG.
- When to test directly. Private wells and some municipal blends vary significantly within a state. For an exact reading, request your utility's Consumer Confidence Report (free by law) or buy a $15 test strip kit.
Data provenance: methodology page.