Water hardness in Arizona
Arizona has a median ambient water hardness of 310 mg/L, which is 18.1 grains per gallon and classes as very hard. That is the middle of 57,699 samples across 15 counties.
This is ambient water, not tap water. These figures come from samples taken from wells, streams and springs by USGS, EPA and state agencies. Municipal utilities treat, blend and sometimes soften water before it reaches a tap, so a city supply can be considerably softer than the ground beneath it. Treat this as a good guide for a private well and an approximate one for city water. Your utility's annual water quality report gives the real number for a municipal tap, and a test strip gives it for yours.
Every monitored county in Arizona
Ranked hardest first. The middle 50% column shows how much the samples within a county vary, which matters more than the median where a county spans two geologies.
| County | mg/L | gpg | Class | Middle 50% | Samples |
|---|---|---|---|---|---|
| Yuma County | 480 | 28 | Very hard | 380 to 810 | 11,417 |
| Maricopa County | 360 | 21 | Very hard | 185 to 621 | 12,510 |
| Mohave County | 340 | 19.9 | Very hard | 230 to 880 | 3,179 |
| La Paz County | 340 | 19.9 | Very hard | 180 to 520 | 2,349 |
| Coconino County | 300 | 17.5 | Very hard | 220 to 450 | 5,409 |
| Pinal County | 266 | 15.5 | Very hard | 140 to 450 | 3,625 |
| Gila County | 255 | 14.9 | Very hard | 140 to 1,120 | 3,523 |
| Yavapai County | 226 | 13.2 | Very hard | 166 to 280 | 4,232 |
| Graham County | 210 | 12.3 | Very hard | 130 to 318 | 1,157 |
| Santa Cruz County | 208 | 12.2 | Very hard | 150 to 340 | 646 |
| Cochise County | 160 | 9.3 | Hard | 95 to 240 | 2,757 |
| Greenlee County | 160 | 9.3 | Hard | 130 to 230 | 1,102 |
| Apache County | 150 | 8.8 | Hard | 56 to 261 | 2,046 |
| Pima County | 131 | 7.7 | Hard | 86 to 224 | 2,280 |
| Navajo County | 130 | 7.6 | Hard | 22 to 280 | 1,467 |
Source: Water Quality Portal (USGS, EPA and state agencies), waterqualitydata.us, retrieved 2026-09-19. 2,904,346 samples across 3,110 counties.
What this means for a household in Arizona
At 18.1 grains per gallon, a family of four would need a softener of about 40,000 grains to regenerate roughly weekly, using around 744 lb of salt a year. Size it for your own household.
15 of these counties include well samples, so the figures are a reasonable guide for private well water there. Municipal supplies in the same counties may be softer, because utilities often blend or treat.
Hardness follows geology rather than borders. Where a county sits on limestone or dolomite the water is hard; on granite, basalt or sandstone it is soft. That is why neighbouring counties in this table can differ by a factor of several.