Water in Arizona.
Arizona's water comes overwhelmingly from the Colorado River (CAP) and deep desert groundwater. Naturally occurring arsenic is widespread in groundwater across the state. Hexavalent chromium contamination from industrial activity is concentrated in the Phoenix metro.
Phoenix and Tucson regularly post arsenic levels above EWG's health-protective guideline.
How Arizona regulates drinking water.
Federal SDWA primacy. State tracks chromium-6 with its own monitoring program. No stricter state MCL for arsenic; relies on federal 10 ppb.
Arizona's water history, in order.
The contamination events, regulatory shifts, and major settlements that define how this state thinks about drinking water today.
- 2006
Federal arsenic MCL drops to 10 ppb; Arizona utilities require massive treatment upgrades.
- 2015
Hexavalent chromium plume documented in Phoenix industrial corridor.
- 2023
Colorado River drought declaration intensifies regional water-supply pressure.
The actual water you drink.
The physical rivers, aquifers, lakes, and reservoirs that feed Arizona's public water systems. Source quality is the foundation of tap quality — and where the long-term protection fights happen.
- riverColorado River (CAP)
Lake Mead/Powell water delivered via the Central Arizona Project.
- reservoirSalt River Project reservoirs
Roosevelt, Apache, Saguaro for Phoenix metro.
- riverVerde River
Joins Salt River for Phoenix metro supply.
- aquiferBasin and Range Aquifers
Deep desert groundwater across rural AZ.
Source-water mix
~60% Colorado River surface water, ~40% groundwater
Major cities served
Phoenix · Tucson · Mesa · Chandler · Scottsdale
Who actually serves the water.
The largest public water systems in Arizona by population served. Click your ZIP after to see the full live EWG report for your specific utility.
- City of Phoenix Water ServicesPhoenix1,650Kserved
- Tucson WaterTucson730Kserved
- Salt River ProjectPhoenix metro· Raw-water provider to multiple cities.Raw-water provider to multiple cities.2,300Kserved
- Mesa Water ResourcesMesa510Kserved
- Chandler Public WorksChandler280Kserved
Where the contamination comes from.
Every state has a different industrial fingerprint. The industries below are the dominant historical and active contamination sources in Arizona's drinking water systems.
Phoenix industrial corridor produced documented hexavalent chromium plumes; mining (copper, uranium) drives heavy-metal exposure across central and southeast AZ. Naturally occurring arsenic from desert geology contaminates groundwater statewide.
What state data flags most consistently.
Drawn from EPA SDWIS sampling records, EWG state summaries, and regional regulatory action over the past five years. Read the full deep dive on each.
Arsenic
A naturally occurring carcinogen. Highest in private wells and the rural Southwest.
Chromium-6 (Hexavalent Chromium)
The Erin Brockovich chemical. A known carcinogen with no federal-specific limit yet.
Trihalomethanes (TTHMs)
Byproducts of chlorinating water. Linked to bladder cancer at chronic exposure.
Nitrate
Fertilizer and animal waste runoff. Acutely dangerous for infants under 6 months.
Risk isn't evenly distributed.
Older adults and immunocompromised residents in groundwater-served rural communities face the highest cumulative arsenic exposure.
~12% on private wells, concentrated in rural northern and southern counties with elevated natural arsenic.
What's coming for Arizona's water.
Tier 2A Colorado River shortage declared 2023 — Arizona faces the largest CAP cutbacks. Aquifer depletion outpaces recharge in most rural basins. Extreme-heat-driven domestic demand stresses delivery infrastructure.
Voluntary statewide
Arizona Department of Environmental Quality provides voluntary screening; participation has expanded since 2019 but remains under 50% of districts.
Five questions for your next Consumer Confidence Report.
Your utility is required to send you a Consumer Confidence Report annually. Most are dense and procedural. These are the questions worth following up on for Arizona specifically.
- 1
Is my utility's arsenic running annual average below the 10 ppb federal MCL?
- 2
Has my utility been impacted by the Colorado River Tier 2A shortage declaration?
- 3
What is my utility doing about hexavalent chromium (Cr-6) — California regulates it; the EPA does not yet.
- 4
Are private wells in my area tested for arsenic, and at what frequency?
Most state regulators allow public records requests for the underlying lab reports behind your CCR — your utility should be able to provide them on request.
What's changed in Arizona water law.
Drinking water regulation moves at the state level as much as the federal level. Below are notable recent bills and regulatory actions specific to Arizona.
- 2023
Arizona Drought Contingency Plan extended; Tier 2A shortage triggers begin.
- 2021
Groundwater management modernization bills considered; comprehensive reform did not pass.
For arsenic and chromium-6 — NSF/ANSI 58 reverse osmosis. For chlorine taste / TTHMs in Phoenix metro, NSF/ANSI 53 carbon block.
We don't recommend brands — the NSF/ANSI certification number matters more than the name on the box.
This is the state. Your address is the answer.
State-level patterns don't tell you about your specific tap. Run your ZIP for the live EWG contaminant report on your utility — or build a personalized Water File for your household.
Source-water mix, utility counts, lead-service-line estimates, and private-well shares are approximate, drawn from EPA SDWIS public data and state primacy-agency summaries. Contaminant rankings reflect EWG state-level monitoring data and regional regulatory action — they are not exhaustive. Timeline events are publicly documented. See methodology for the full sourcing. Search EPA SDWIS for Arizona