How we get our data
We use only figures that a public water authority has published itself for its own customers. Here is every authority we use, with a link to its website, the kind of document each figure comes from, and how we turn it into a softener size.
How we size a softener
We multiply the number of people in the home by 75 gallons per person per day, then by the hardness in grains per gallon. That gives the hardness the softener removes each day. We pick the smallest standard size (24,000 to 80,000 grains) that lasts about 7 days between recharges, and estimate salt at 3,300 grains removed per pound of salt. The dial setting is the hardness rounded up.
How we describe hardness
We use the U.S. Geological Survey scale: soft below 3.5 grains per gallon, moderately hard to 7, hard to 10.5 and very hard above that. We call 17 and above “extremely hard”; that last split is our own, because so much Valley water sits above 10.5. One grain per gallon equals 17.1 milligrams per litre (mg/L).
What the figures can’t tell you
Utilities publish ranges, averages or zone figures. Hardness changes by street and season as utilities switch between river, canal and well water. A home test kit gives your exact number, and the calculator uses it in place of the city figure.
Using the figures
Each city’s figure is used on its own city page, in the Valley hardness table and in the size chart, so they always match.
Every water utility we use
| Water authority | Type of source | Areas | Hardness range | Last checked |
|---|---|---|---|---|
| City of Phoenix Water Services Department The City of Phoenix department that runs Phoenix's public drinking-water system. | Annual water quality report. Every community water system in the U.S. must publish one each year under the federal Safe Drinking Water Act, so it is the utility’s own official record of what is in its water. Data year: 2025. | Phoenix | 10 to 17.6 grains per gallon | 15 October 2026 |
| Scottsdale Water (City of Scottsdale) The City of Scottsdale's water utility, which treats and delivers the city's drinking water. | Annual water quality report. Every community water system in the U.S. must publish one each year under the federal Safe Drinking Water Act, so it is the utility’s own official record of what is in its water. Data year: 2026 (2025 data). | South of Indian School Rd; Between Indian School Rd and Chaparral Rd; North of Chaparral Rd | 13 to 17 grains per gallon | 15 October 2026 |
| City of Mesa Water Resources Department The City of Mesa department that supplies the city's drinking water. | Annual water quality report. Every community water system in the U.S. must publish one each year under the federal Safe Drinking Water Act, so it is the utility’s own official record of what is in its water. Data year: 2025. | City Zone; Eastern and Southern Zones | 12 to 16 grains per gallon | 15 October 2026 |
| City of Chandler The city government that runs Chandler's public water system, including its surface water treatment plant and 32 groundwater wells. | Water quality questions-and-answers page published by the utility for its own customers. Data year: undated web page. | Chandler | 5 to 20 grains per gallon | 15 October 2026 |
| City of Peoria Water Services Department The City of Peoria department that runs the city's water supply, water quality testing, reclaimed water and conservation programs. | Hardness study carried out by the utility itself, with the results published as public map data. Data year: 2020. | Peoria | 5.1 to 19.7 grains per gallon | 15 October 2026 |
| Town of Gilbert Public Works (Water) The Town of Gilbert's water division, which treats and tests the town's drinking water. | Annual water quality report. Every community water system in the U.S. must publish one each year under the federal Safe Drinking Water Act, so it is the utility’s own official record of what is in its water. Data year: 2026 (2025 data). | Gilbert | 6.6 to 17.5 grains per gallon | 16 October 2026 |
| City of Glendale Water Services Department The City of Glendale department that treats and delivers the city's drinking water and handles wastewater and stormwater. | Annual water quality report. Every community water system in the U.S. must publish one each year under the federal Safe Drinking Water Act, so it is the utility’s own official record of what is in its water. Data year: 2026 (2025 data). | Glendale | 5.4 to 18.5 grains per gallon | 16 October 2026 |
| City of Tempe Water Utilities The City of Tempe utility that provides water, wastewater and stormwater services for Tempe and Guadalupe. | Annual water quality report. Every community water system in the U.S. must publish one each year under the federal Safe Drinking Water Act, so it is the utility’s own official record of what is in its water. Data year: 2026 (2025 data). | Tempe | 10.4 to 32.6 grains per gallon | 16 October 2026 |
| City of Surprise Water Resource Management The City of Surprise department that runs four public water systems supplied by city wells. | Annual water quality report. Every community water system in the U.S. must publish one each year under the federal Safe Drinking Water Act, so it is the utility’s own official record of what is in its water. Data year: 2026 (2025 data). | Mountain Vista water system; Desert Oasis water system; Surprise Foothills water system; Circle City water system | 2.6 to 11.1 grains per gallon | 16 October 2026 |
| Town of Queen Creek Water Services The Town of Queen Creek's water division, which runs the town's wells and water distribution system. | Water quality questions-and-answers page published by the utility for its own customers. Data year: undated web page. | Queen Creek | 6 to 17 grains per gallon | 16 October 2026 |
| EPCOR Water Arizona (Chaparral City water system) The private water company that serves the Town of Fountain Hills and parts of Scottsdale through its Chaparral City water system. | Annual water quality report. Every community water system in the U.S. must publish one each year under the federal Safe Drinking Water Act, so it is the utility’s own official record of what is in its water. Data year: 2025 (hardness sampled in 2024). | Fountain Hills | about 16 grains per gallon | 16 October 2026 |
No company supplies or pays for these figures.