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Arizona water profile

Nitrate in Arizona community water systems

Arizona's higher nitrate gathers in the irrigated central corridor — the Phoenix–Pinal–Tucson basin-fill aquifers under some of the most intensive irrigated agriculture in the Southwest. See where the pattern concentrates and what each reporting system measured in the three years from August 9, 2023 to August 9, 2026.

Browse all 742 Arizona systems →

Search by the utility or system name shown on a water bill. Example: City of Casa Grande Water. Private wells are not in this inventory.

99%
of the state’s 749 active community water systems have a current result here
742
systems with a current nitrate result
7,094,412
people served by those reporting systems
12.5%
of reporting systems at or above 5 mg/L
How to read these numbers Each system is placed into a band by its most recent reported result within a rolling three-year window. The bands describe how strongly human activity, read from nitrate, has marked a water source; they are not a safety verdict. Figures describe system reporting, not nitrate measured at an individual tap.

How Arizona's systems fall across the five bands

Most systems report below 3 mg/L

Natural background
0.00–0.99 mg/L as N
304 systems · 2,927,805 served
Human impact likely
1.00–2.99 mg/L as N
232 systems · 1,000,947 served
Human impact clear
3.00–4.99 mg/L as N
113 systems · 814,194 served
Health-study range
5.00–9.99 mg/L as N
88 systems · 2,350,708 served
Above the federal limit
10.00 mg/L and above
5 systems · 758 served

Each system appears in one band only, placed by its most recent reported result in the current three-year window. Counts sit beside people served so a small number of larger systems cannot hide behind a row of tiny ones. Of the 93 systems reporting 5 mg/L or more, 39 stayed at or above 5 across the whole three-year range; the other 54 reached it only on a high sample and otherwise ran lower.

Most recent reading Jul 2026; the typical system was last tested around Feb 2026. 716 systems sampled their own water; 26 systems carry a supplier’s result.

The named systems

Every reading here belongs to a utility with a name

Highest recent readings
SystemMost recent resultBandBased onPeople served
Cs Carter Water Company33.00 mg/LApr 2026a high point — runs lowerAbove the federal limit4 samples28
Papago Butte Dwid32.40 mg/LApr 2026Above the federal limit13 samples530
Grandview Water Company13.70 mg/LJun 2026a high point — runs lowerAbove the federal limit12 samples50
Softwinds Mobile Home Park11.50 mg/LApr 2026Above the federal limit18 samples70
Mountain Vu Rv Court10.10 mg/LJul 2026Above the federal limit12 samples80
New Saddleback Vista9.57 mg/LApr 2026Health-study range15 samples100
Goodyear Water Department9.36 mg/LApr 2026a high point — runs lowerHealth-study range61 samples50,001
Olive Avenue Hoa9.22 mg/LMay 2026Health-study range14 samples25
Largest systems
SystemMost recent resultBandBased onPeople served
Phoenix City Of0.80 mg/LJun 2026Natural background81 samples1,695,000
Tucson City Of5.28 mg/LJun 2026a high point — runs lowerHealth-study range261 samples732,906
Mesa City Of5.35 mg/LJun 2026a high point — runs lowerHealth-study range124 samples466,000
Gilbert, Town Of7.60 mg/LMay 2026a high point — runs lowerHealth-study range143 samples247,600
Chandler City Of0.25 mg/LJun 2026Natural background154 samples247,328

Each result shows its date and what it rests on, so a lone sample is never taken for a settled measurement. A single high sample is not a complete account of what a household drinks.

Where higher nitrate concentrates

Higher results gather in the irrigated central corridor

Human impact is clear on drinking water served in twelve of Arizona’s 15 counties. Each is shaded by how many of its systems reported 3.00 mg/L as N or above. Shading counts systems, not severity — a county with many small utilities can outrank one holding a single larger system that reads higher. The table beside the map splits the two bands so that difference stays visible.

AZ counties shaded by number of community water systems reporting nitrate at or above 3.00 mg/L as NCounties are shaded by how many community water systems reported nitrate at or above 3.00 mg/L as N in the three years from August 9, 2023 to August 9, 2026. The same counts appear in the table below this map.Mohave County — 16 systems at 3.00–4.99 mg/L as N; 5 systems at 5.00 mg/L as N or aboveSanta Cruz County — 7 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveCoconino County — 2 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveLa Paz County — 4 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveGila County — 8 systems at 3.00–4.99 mg/L as N; 3 systems at 5.00 mg/L as N or abovePima County — 23 systems at 3.00–4.99 mg/L as N; 18 systems at 5.00 mg/L as N or abovePinal County — 12 systems at 3.00–4.99 mg/L as N; 33 systems at 5.00 mg/L as N or aboveYuma County — 2 systems at 3.00–4.99 mg/L as N; 3 systems at 5.00 mg/L as N or aboveMaricopa County — 22 systems at 3.00–4.99 mg/L as N; 23 systems at 5.00 mg/L as N or aboveGraham County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveCochise County — 5 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveYavapai County — 11 systems at 3.00–4.99 mg/L as N; 6 systems at 5.00 mg/L as N or above
none1–23–56–1112–2526+Number of drinking water systems reporting ≥3.00 mg/L NO₃–N per county as of August 9, 2026

Pinal leads this layer with 33 reporting systems, followed by Maricopa, Pima, Yavapai. Higher results gather in the irrigated central corridor.

Counties with the most systems at or above 3 mg/L as N
County3–4.99≥5Total ≥3
Maricopa222345
Pinal123345
Pima231841
Mohave16521
Yavapai11617

Counts use each system's most recent reported result in the current three-year window. A system appears in only one of the two bands.

Find a specific Arizona system

What the statewide pattern says

A basin-fill pattern, with a desert nuance

Arizona's higher nitrate tracks its basin-fill aquifers where irrigated agriculture and urban growth load nitrogen over deep alluvial fill — with Pinal County's irrigated corridor at the center — while parts of the desert carry a natural background worth knowing about.

Arizona's aquifers are deep basin fill between mountain ranges, and USGS's Southwest-wide assessment found nitrate at or above the federal limit in about 11 percent of basin-fill samples, with predicted exceedance tracking how much of the land above is developed for agriculture or urban use — rising to nearly half where the land is fully developed (Beisner, Anning and others, USGS SIM 3234). Fertilizer and livestock manure are the named sources in agricultural settings (Nolan and Hitt, 2006).

The map's center of gravity — Pinal County, between Phoenix and Tucson — is the state's irrigated-cotton and dairy corridor, where decades of heavy irrigation have left a legacy nitrate load in the vadose zone that continues to reach groundwater even as surface practices change (Arizona DEQ, Pinal Active Management Area). Maricopa and Pima add the urban fringe: fertilizer, reclaimed-water irrigation, and septic on the same basin fill.

One nuance is distinctly Arizonan: across parts of the Sonoran Desert, nitrate between 2 and 5 mg/L appears to be natural — nitrogen fixed by desert legumes over undisturbed basin fill — so a modest reading there is not automatically a human fingerprint (USGS SIM 3234). The supported source reading is agricultural and urban nitrogen on basin fill, against a locally elevated natural desert background — not a certified source at any individual system. Arizona basin-fill also carries geogenic arsenic and uranium, so the co-occurrence caution applies (Dubrovsky and others, 2010).

The general science — how nitrate moves, why some ground is vulnerable, and why the legacy lingers — is laid out with its sources on Where nitrate comes from.

Questions this page answers

What the Arizona pattern does—and does not—say

Where does nitrate concentrate in Arizona community water systems?

Pinal leads this layer with 33 reporting systems, followed by Maricopa, Pima, Yavapai. Higher results gather in the irrigated central corridor.

Is Arizona nitrate always from farming?

No. Irrigated agriculture and urban growth explain most elevated readings, but parts of the Sonoran Desert carry a natural 2 to 5 mg/L background from nitrogen-fixing desert legumes. Below roughly 2 mg/L is the usual undeveloped background; above that, development is the likely driver — with the desert exceptions noted.

Can this page say the source is agriculture?

At the zone level, mostly — fertilizer and livestock manure in the irrigated corridor, urban nitrogen on the fringes — but Arizona adds a documented natural desert background in the 2 to 5 mg/L range that other states lack. No reading certifies a source at an individual system.

Does a high public-system result mean a nearby private well is high?

No. It is a local sentinel, not a well-specific result. It shows that nitrogen and a transport pathway have reached groundwater in the area; a certified-lab test is still the only way to know a specific private well.

Sources and provenance

What this page rests on

  1. NitrateSmart inventory: 742 Arizona community water systems with a current nitrate result in the three years from August 9, 2023 to August 9, 2026. Figures count people served by reporting systems, not measured tap exposure.
  2. Nolan BT, Hitt KJ (2006). Vulnerability of Shallow Groundwater and Drinking-Water Wells to Nitrate in the United States. Environmental Science & Technology 40(24):7834–7840.
  3. Dubrovsky NM, and others (2010). Nutrients in the Nation's Streams and Groundwater, 1992–2004. USGS Circular 1350.
  4. Beisner KR, Anning DW, and others (2012). Maps of estimated nitrate and arsenic concentrations for basin-fill aquifers of the Southwest Principal Aquifers study area. USGS Scientific Investigations Map 3234 — nitrate at or above the federal limit in ~11% of samples; Sonoran Desert natural 2–5 mg/L background.
  5. Arizona Department of Environmental Quality. Pinal Active Management Area groundwater fact sheet — the irrigated-corridor setting behind the map’s center of gravity.