Arizona Water Hardness by County
Water in Arizona has a median hardness of 300 mg/L as CaCO₃ — "very hard" on the USGS scale — based on 59,446 measurements at 13,756 monitoring stations. Yuma County has the state's hardest measured water (470 mg/L); Navajo County the softest (120.5). Rank: #4 of the 50 states and D.C.
Arizona water hardness map — what the numbers mean. Data verified 2026-07-22.
Every one of Arizona's 15 measured counties tests hard or harder: 10 rank very hard and 5 rank hard. The hardest are Yuma County (470 mg/L), Maricopa County (359), and La Paz County (340). Even Navajo County, the softest measured area in the state, reads 120.5 mg/L — still hard on the USGS scale.
About 100% of Arizona's roughly 7.3 million residents in counties with gate-passing hardness data live where tap water is hard or worse.
Statewide, Arizona's median works out to 17.5 grains per gallon and ranks #4 of the 50 states and D.C. Across 59,446 measurements at 13,756 stations — 14,513 of them since 2000 — the middle 80% of readings fall between 83 and 929.6 mg/L. The public record runs from 1917 to 2026.
See where Arizona sits nationally on the national map, or what its number means on the hardness scale.
Download the Arizona water hardness map (PNG) — Water hardness by county in Arizona: 15 counties mapped from USGS/EPA data, statewide median 300 mg/L (very hard); darker counties have harder water.
By county
Water hardness by county
The table lists all 15 measured Arizona counties, hardest first. Their medians span 470 mg/L in Yuma County to 120.5 in Navajo County — a 3.9× range.
| County | Median | Band | Results | Sites | Newest |
|---|---|---|---|---|---|
| Yuma County | 470 | Very hard | 11,402 | 801 | 2023 |
| Maricopa County | 359 | Very hard | 12,682 | 2,429 | 2025 |
| La Paz County | 340 | Very hard | 2,413 | 556 | 2023 |
| Mohave County | 340 | Very hard | 3,469 | 1,049 | 2023 |
| Coconino County | 300 | Very hard | 5,349 | 797 | 2023 |
| Pinal County | 260 | Very hard | 3,771 | 1,102 | 2025 |
| Gila County | 239 | Very hard | 3,685 | 644 | 2023 |
| Yavapai County | 224 | Very hard | 4,325 | 1,213 | 2026 |
| Santa Cruz County | 207.5 | Very hard | 754 | 266 | 2024 |
| Graham County | 206 | Very hard | 1,292 | 439 | 2023 |
| Cochise County | 160 | Hard | 3,145 | 1,428 | 2022 |
| Greenlee County | 160 | Hard | 1,187 | 236 | 2017 |
| Apache County | 150 | Hard | 2,038 | 841 | 2023 |
| Pima County | 134 | Hard | 2,440 | 1,291 | 2023 |
| Navajo County | 120.5 | Hard | 1,483 | 658 | 2023 |
| 11 additional results from sites without county attribution (not shown). | |||||
ZIP codes
ZIP codes in Arizona
The ZIP codes below are grouped by the Arizona county they fall in. Each ZIP takes its county's measured median — shown in the group header — so this is a ZIP-to-county guide, not a separate reading for every ZIP. To check the water system serving a specific address, use the lookup.
Yuma County · 470 mg/L · Very hard
85336†85347†85349†85350†85352†85356†8536485365†85367†
Maricopa County · 359 mg/L · Very hard
8500385004850068500785008850098501285013850148501585016850178501885019850208502185022850238502485026850278502885029850318503285033850348503585037850408504185042850438504485045850488505085051850538505485083850858508685087†8520185202852038520485205852068520785208†8520985210852128521385215†852248522585226†852338523485236852488524985250†85251852538525485255†85256†852578525885259†8526085262†85263†85264†85266852688528185282852838528485286852958529685297852988530185302853038530485305853068530785308853098531085320†85322†8532385326†8532985331†85333†8533585337†8533885339†8534085343†85345853518535385354†8535585361†8536385373†85374853758537785378†85379853818538285383†853878538885390†853928539585396†85545†
La Paz County · 340 mg/L · Very hard
85325†85328†85334†85344†85346†85348†85357†85371†
Mohave County · 340 mg/L · Very hard
85360†86021†86401†8640386404†86406†86409†86411†8641386426†86429†86431†86432†86433†86434†86436†86437†86438†86440†864418644286443†86444†86445†
Coconino County · 300 mg/L · Very hard
85931†86001†86003†86004†86005†8601186015†86016†86017†86018†86020†86022†86023†86024†86030†86035†86036†86038†86040†86044†86045†86046†86052†86053†86320†86435†
Pinal County · 260 mg/L · Very hard
85118†85119†8512085121†8512285123†8512885131†85132†85137†8513885139†85140†85141†8514285143†85145†85147†85172851738519185192†8519385194†85618†85623†85631†85658†85739†
Gila County · 239 mg/L · Very hard
8513585501†8553285539†8554185544†85550†85553†85554†85941†
Yavapai County · 224 mg/L · Very hard
85324†85332†85342†85362†86301†86303†86305†863138631486315†86321†86322†86323†86324†86325†86326†86327†86329†86331†86332†86333†86334†86335†86336†86337†86338†86343†86351
Santa Cruz County · 207.5 mg/L · Very hard
85611†85621†85624†85637†85640†8564685648
Graham County · 206 mg/L · Very hard
85530†8553185535†85536†85542†8554385546†85551†85552†85643†
Cochise County · 160 mg/L · Hard
85602†8560385605†85606†85607†85608†85609†85610†85613†8561585616†85617†8562085625†85626†85627†85630†85632†85635†85638†85650†
Greenlee County · 160 mg/L · Hard
85533†85534†85540†85922†
Apache County · 150 mg/L · Hard
85920†85924†85925†85927†85930†85932†85936†85938†8594086028†86502†86503†86504†86505†86506†86507†86508†86511†86512†86514†86520†86535†86538†86540†86544†86545†86547†86556†87328†
Pima County · 134 mg/L · Hard
85321†85341†85601†85614†85619†85622†85629†85633†85634†85639†85641†85645†85653†85654857018570485705857068570785708857098571085711857128571385714857158571685718857198572185723857248572685730†8573485735†85736†85737857418574285743†85745†85746†857478574885749857508575585756†85757
Navajo County · 120.5 mg/L · Hard
8590185902†85911†85912†85923†85926†85928†8592985933†8593485935†85937†8593985942†86025†8602986031†86032†86033†86034†86039†86042†8604386047†86054†86510†
† 243 ZIP codes are not served by a mapped community water system — most are private-well areas. See well water hardness.
Source
Groundwater vs surface water
Arizona's surface water measures harder than its groundwater — 330 mg/L across 32,971 samples versus 270 across 26,428, about 1.2× harder. For well owners that is the better side of a hard bargain: at 270 mg/L, Arizona groundwater is still very hard, and most of the state's drinking water is pumped from it. Groundwater readings there run 69.2 to 889 mg/L across the middle 80% of samples. The comparison draws on 11,237 groundwater and 2,509 surface-water monitoring sites; 691 readings above 2,000 mg/L were logged but held out of the medians as outliers.
Groundwater (wells)
270 mg/L as CaCO₃ · 26,428 results at 11,237 stations.
Surface water (rivers, lakes)
330 mg/L as CaCO₃ · 32,971 results at 2,509 stations.
Surface water measures about 1.2× harder than groundwater here.
Chemistry
Water chemistry in Arizona
Beyond the hardness number, Arizona's water carries a fuller chemical signature — here is how its measured parameters compare to national benchmarks.
TDS
349 mg/L · n=13,537
349 mg/L — about 1.5× the national county median of 226, consistent with hard, mineral-rich water.
pH
8 pH · n=15,423
pH 8 — within the EPA secondary range of 6.5–8.5, on the alkaline side.
Alkalinity
166 mg/L as CaCO3 · n=14,416
166 mg/L — substantial buffering capacity, which resists pH swings.
Calcium : Magnesium
53 : 19 mg/L ≈ 2.79 : 1 · n=19,899
Calcium is about 63% of Arizona's hardness (53 mg/L Ca to 19 mg/L Mg), a little more magnesium-rich than the national ~68% calcium share.
Parameter medians may include a small share of quality-control samples; the hardness lane is fully QC-filtered.
Aquifers
Major aquifers under Arizona
Two aquifer systems supply much of Arizona's measured groundwater.
- Basin and Range basin-fill aquifers — median 530 mg/L across 1,110 samples at 471 sites: very hard.
- Colorado Plateaus aquifers — median 95.6 mg/L across 177 samples at 35 sites: moderately hard.
Together these systems account for 1,287 measured samples at 506 sites. Aquifer medians pool samples across a whole system and can mask local variation — see the national aquifer map for how these compare across states.
Trend
Hardness over time
Arizona's decade median moved from 430 mg/L in the 1920s to 271 in the 2020s. Over the series, the decade median peaked at 490 mg/L in the 1930s and bottomed at 200 in the 2000s. Decade medians reflect where and what agencies sampled in each era, not just changes in the water itself.
Scale
Where Arizona sits on the scale
On the USGS scale, Arizona's 300 mg/L is very hard — 17.5 grains per gallon, well above the 180 mg/L very-hard cutoff — among the hardest water measured in the US.
At 300 mg/L (17.5 gpg), water-softener owners in Arizona typically set their unit to this hardness — settings calculator.
Questions
Frequently asked questions
- Is Arizona's water hard?
- Arizona's median hardness is 300 mg/L as CaCO₃, "very hard" on the USGS scale and 2.14× the national county median of 140 mg/L. About 100% of residents in measured counties have hard-or-worse water.
- Which county in Arizona has the hardest water?
- Yuma County, with a median of 470 mg/L as CaCO₃ across 11,402 measurements. Even the softest, Navajo County at 120.5 mg/L, is still "hard" on the USGS scale.
- Is well water harder than city water in Arizona?
- Surface water measures harder here — about 1.2× the groundwater — so wells tend to run softer (groundwater 270 vs surface water 330 mg/L).
- How do I find my exact hardness in Arizona?
- Search your ZIP on the lookup tool, read your utility's Consumer Confidence Report, or test at home with a kit.
- Is Arizona's water harder than the national average?
- Yes. Arizona's median of 300 mg/L is 2.14× the national county median of 140 mg/L, and Arizona ranks #4 of the 50 states and D.C.
Compare
States with similar hardness
Two states measure closest to Arizona's 300 mg/L: Iowa at 310 mg/L and North Dakota at 310 mg/L. Arizona measures harder than 94% of states. Browse the full ranking on the statistics page.
More: hardness scale · check your address · national statistics · the national map.
By Marko Visic, MPharm, BSc Physics. Source: USGS/EPA Water Quality Portal — 59,446 Arizona measurements. Data last verified . Methodology.
Cite this page: “Arizona Water Hardness by County.” Hard Water Map. Retrieved 2026-07-22, https://hardwatermap.com/water-hardness/arizona/