Most softeners ask for hardness in grains per gallon (gpg). Set it too low and you get hard water. Set it too high and you waste salt and water.
Step 1: Get your utility's number
- Tucson: the city's interactive map shows grains per gallon from a sample point near your address.2
- Las Vegas: the water district tells customers to set softeners for 280 ppm, or 16 gpg.3
- Mesa: the city says hardness ranges from 12 to 22 gpg depending on your water source.4
- San Diego: the 2025 report shows treatment-plant averages of 13.8–14.2 gpg.5
Step 2: Convert ppm (mg/L) to gpg
Divide by 17.1. That's the conversion Tucson Water gives.1 Example: 280 ppm ÷ 17.1 ≈ 16.4 gpg.
Step 3: Check the manual
Manufacturers program softeners differently. Follow your model's manual, and if your city's figure is a range, ask your installer to test your water. Not sure you need a softener at all? Read softener vs. RO.
Sources
- Tucson Water: water quality parameter explanation table
- City of Tucson: interactive water quality lookup
- LVVWD Water Quality Report (softener setting guidance)
- City of Mesa: hard water
- City of San Diego 2025 Annual Drinking Water Quality Report
Last reviewed Oct 13, 2026. This is general information, not professional advice. Confirm figures with your utility and installer.