Oklahoma
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Oklahoma water profile

Nitrate in Oklahoma community water systems

Oklahoma's nitrate map splits the state in two: quiet east of the Cross Timbers, and a striking band of high-reporting systems across the irrigated west — Garfield, Beckham, Washita, Woodward, Kingfisher. 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 863 Oklahoma systems →

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

97%
of the state’s 889 active community water systems have a current result here
863
systems with a current nitrate result
3,637,673
people served by those reporting systems
16.1%
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 Oklahoma's systems fall across the five bands

Most systems report below 3 mg/L

Natural background
0.00–0.99 mg/L as N
565 systems · 3,098,600 served
Human impact likely
1.00–2.99 mg/L as N
109 systems · 278,690 served
Human impact clear
3.00–4.99 mg/L as N
50 systems · 33,177 served
Health-study range
5.00–9.99 mg/L as N
119 systems · 213,680 served
Above the federal limit
10.00 mg/L and above
20 systems · 13,526 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 139 systems reporting 5 mg/L or more, 101 stayed at or above 5 across the whole three-year range; the other 38 reached it only on a high sample and otherwise ran lower.

Most recent reading Jun 2026; the typical system was last tested around Jan 2026. 545 systems sampled their own water; 318 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
Dill City18.00 mg/LMay 2026a high point — runs lowerAbove the federal limit14 samples526
Canadian Co Rwd # 115.00 mg/LJun 2026Above the federal limit12 samples750
Okarche Rwd, Inc14.10 mg/LMay 2026Above the federal limit12 samples250
Thirsty Water Corp12.70 mg/LFeb 2026a high point — runs lowerAbove the federal limit10 samples81
Tipton11.90 mg/LApr 2025Above the federal limit*1 sample916
Grandfield11.60 mg/LApr 2026a high point — runs lowerAbove the federal limit22 samples1,110
Devol11.60 mg/LApr 2026a high point — runs lowerAbove the federal limitinherited from supplier150
Randlett Pwa11.60 mg/LApr 2026a high point — runs lowerAbove the federal limitinherited from supplier320
Largest systems
SystemMost recent resultBandBased onPeople served
Oklahoma City0.68 mg/LJan 2025Natural background8 samples644,000
Tulsa0.10 mg/LJan 2026Natural background8 samples413,000
Broken Arrow Municipal Authority0.08 mg/LSep 2025Natural background3 samples116,330
Norman Utilities Authority0.48 mg/LApr 2026Natural background16 samples104,868
Lawton0.79 mg/LMar 2026Natural background6 samples92,757

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

A striking western band

Human impact is clear on drinking water served in 45 of Oklahoma’s 77 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.

OK 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.Blaine County — 3 systems at 3.00–4.99 mg/L as N; 4 systems at 5.00 mg/L as N or aboveComanche County — 1 system at 3.00–4.99 mg/L as N; 3 systems at 5.00 mg/L as N or aboveBeckham County — 0 systems at 3.00–4.99 mg/L as N; 9 systems at 5.00 mg/L as N or aboveKingfisher County — 1 system at 3.00–4.99 mg/L as N; 7 systems at 5.00 mg/L as N or aboveCuster County — 0 systems at 3.00–4.99 mg/L as N; 3 systems at 5.00 mg/L as N or aboveGreer County — 0 systems at 3.00–4.99 mg/L as N; 7 systems at 5.00 mg/L as N or aboveGrady County — 4 systems at 3.00–4.99 mg/L as N; 2 systems at 5.00 mg/L as N or aboveCreek County — 0 systems at 3.00–4.99 mg/L as N; 2 systems at 5.00 mg/L as N or aboveAlfalfa County — 0 systems at 3.00–4.99 mg/L as N; 5 systems at 5.00 mg/L as N or aboveCotton County — 0 systems at 3.00–4.99 mg/L as N; 2 systems at 5.00 mg/L as N or aboveCleveland County — 2 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveJefferson County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveWoods County — 0 systems at 3.00–4.99 mg/L as N; 7 systems at 5.00 mg/L as N or aboveWoodward County — 2 systems at 3.00–4.99 mg/L as N; 7 systems at 5.00 mg/L as N or aboveMcIntosh County — 2 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveGarfield County — 0 systems at 3.00–4.99 mg/L as N; 14 systems at 5.00 mg/L as N or aboveEllis County — 2 systems at 3.00–4.99 mg/L as N; 2 systems at 5.00 mg/L as N or aboveJackson County — 0 systems at 3.00–4.99 mg/L as N; 5 systems at 5.00 mg/L as N or aboveTexas County — 4 systems at 3.00–4.99 mg/L as N; 4 systems at 5.00 mg/L as N or aboveLogan County — 0 systems at 3.00–4.99 mg/L as N; 7 systems at 5.00 mg/L as N or aboveGarvin County — 1 system at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveKiowa County — 1 system at 3.00–4.99 mg/L as N; 3 systems at 5.00 mg/L as N or abovePawnee County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveJohnston County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveOklahoma County — 1 system at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or abovePayne County — 1 system at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveHughes County — 2 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or abovePontotoc County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveStephens County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveDelaware County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveHarmon County — 0 systems at 3.00–4.99 mg/L as N; 3 systems at 5.00 mg/L as N or aboveCanadian County — 1 system at 3.00–4.99 mg/L as N; 2 systems at 5.00 mg/L as N or aboveTillman County — 0 systems at 3.00–4.99 mg/L as N; 4 systems at 5.00 mg/L as N or aboveBryan County — 4 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveNoble County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveDewey County — 2 systems at 3.00–4.99 mg/L as N; 2 systems at 5.00 mg/L as N or aboveRoger Mills County — 1 system at 3.00–4.99 mg/L as N; 3 systems at 5.00 mg/L as N or aboveWashita County — 0 systems at 3.00–4.99 mg/L as N; 9 systems at 5.00 mg/L as N or aboveCaddo County — 3 systems at 3.00–4.99 mg/L as N; 5 systems at 5.00 mg/L as N or aboveCimarron County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveGrant County — 1 system at 3.00–4.99 mg/L as N; 3 systems at 5.00 mg/L as N or aboveMarshall County — 1 system at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveHarper County — 1 system at 3.00–4.99 mg/L as N; 2 systems at 5.00 mg/L as N or aboveBeaver County — 2 systems at 3.00–4.99 mg/L as N; 3 systems at 5.00 mg/L as N or aboveMajor County — 1 system at 3.00–4.99 mg/L as N; 3 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

Garfield leads this layer with 14 reporting systems, followed by Beckham, Washita, Greer. A striking western band.

Counties with the most systems at or above 3 mg/L as N
County3–4.99≥5Total ≥3
Garfield01414
Beckham099
Washita099
Woodward279
Caddo358

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 Oklahoma system

What the statewide pattern says

Irrigated red-bed country

Western Oklahoma’s Permian sandstone and alluvial aquifers sit under irrigated agriculture, and state investigations have measured nitrate above the federal limit there for decades — the public-system map shows it county by county.

The western aquifers are working irrigation water. In the Rush Springs aquifer — red Permian sandstone beneath Caddo, Custer, Washita and neighboring counties — 91 percent of groundwater use is irrigation, and the state water board’s investigation found 13 of its samples above the 10 mg/L federal nitrate limit, a mean of 6.6 mg/L, and a maximum of 59.2 mg/L, with inorganic fertilizer identified as the major contributor (Oklahoma Water Resources Board, 2015).

It is not new. An earlier USGS study of the same aquifer reported a mean nitrate of 14.3 mg/L — above the federal limit as an average — and 28–31 mg/L in wells near a wastewater lagoon, traced to commercial fertilizer (Becker and Runkle, 1998). The aquifer recharges from rainfall through sandy soils, so what is spread on fields reaches the water table.

The public-system map on this page runs beyond the studied block: Garfield County (Enid) and its neighbors sit on terrace and alluvial aquifers over the same Permian red beds, and their systems report high at rates that match the Rush Springs picture. The published investigations cover the Rush Springs block directly; for the counties farther north and west this page reads the public-system data as the signal and the red-bed irrigation setting as the supported mechanism, not a certified per-county source.

The supported source reading is fertilizer nitrogen on irrigated red-bed and alluvial aquifers — not a certified source at any individual system, and the strongest regional pattern in this batch of states (Nolan and Hitt, 2006).

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 Oklahoma pattern does—and does not—say

Where does nitrate concentrate in Oklahoma community water systems?

Garfield leads this layer with 14 reporting systems, followed by Beckham, Washita, Greer. A striking western band.

Why is western Oklahoma's nitrate so much higher than the east?

Geology plus land use. The west drinks from Permian sandstone and alluvial aquifers that recharge through sandy soils under irrigated farmland; the state water board measured a 6.6 mg/L mean in the Rush Springs aquifer with fertilizer the major contributor. The wetter east relies more on surface water and deeper, older groundwater.

How long has western Oklahoma had this problem?

Decades. A 1998 USGS study of the Rush Springs aquifer reported a mean nitrate of 14.3 mg/L — above the federal limit as an average. The state's 2015 reinvestigation still found 13 samples above the limit and a maximum of 59.2 mg/L, so the pattern is structural, not a recent spike.

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: 863 Oklahoma 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. Oklahoma Water Resources Board (2015). Hydrologic Investigation Report of the Rush Springs Aquifer — 13 samples above the 10 mg/L MCL, mean 6.6 mg/L, maximum 59.2 mg/L; inorganic fertilizer the major contributor; irrigation 91% of groundwater use.
  5. Becker CJ, Runkle DL (1998). Steady-State Simulation of Ground-Water Flow in the Rush Springs Aquifer, Western Oklahoma. USGS Water-Resources Investigations Report 98-4082 — reported mean nitrate of 14.3 mg/L in the aquifer.