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Iowa water profile

Nitrate in Iowa community water systems

Most Iowa community water systems report nitrate below 3 mg/L. The systems that run higher are not spread evenly: they concentrate in the intensively tile-drained farm counties of the north-central Des Moines Lobe, with a second setting in the karst northeast. 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 1,060 Iowa systems →

Search by the utility or system name shown on a water bill. Example: Des Moines Water Works. Private wells are not in this inventory.

98%
of the state’s 1,078 active community water systems have a current result here
1,060
systems with a current nitrate result
2,941,052
people served by those reporting systems
9.8%
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 Iowa's systems fall across the five bands

Most systems report below 3 mg/L

Natural background
0.00–0.99 mg/L as N
697 systems · 1,318,967 served
Human impact likely
1.00–2.99 mg/L as N
168 systems · 521,560 served
Human impact clear
3.00–4.99 mg/L as N
91 systems · 342,334 served
Health-study range
5.00–9.99 mg/L as N
103 systems · 758,075 served
Above the federal limit
10.00 mg/L and above
1 system · 116 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 104 systems reporting 5 mg/L or more, 9 stayed at or above 5 across the whole three-year range; the other 95 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. 809 systems sampled their own water; 251 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
Dawson Water Works11.00 mg/LJun 2026a high point — runs lowerAbove the federal limit20 samples116
Union Water Supply9.90 mg/LMar 2026a high point — runs lowerHealth-study range7 samples399
Waverly Water Department9.20 mg/LJun 2026Health-study range96 samples10,394
River Oaks Development9.05 mg/LJun 2026a high point — runs lowerHealth-study rangeinherited from supplier215
Deer Hunters Run9.05 mg/LJun 2026a high point — runs lowerHealth-study rangeinherited from supplier78
Xenia Rwd (Des Moines)9.05 mg/LJun 2026a high point — runs lowerHealth-study rangeinherited from supplier12,860
Truro Waterworks9.05 mg/LJun 2026a high point — runs lowerHealth-study rangeinherited from supplier525
Dmww-Greenbrier Estates9.05 mg/LJun 2026a high point — runs lowerHealth-study rangeinherited from supplier300
Largest systems
SystemMost recent resultBandBased onPeople served
Des Moines Water Works2.81 mg/LJan 2025Human impact likely49 samples246,055
Iowa-American Wtr Co-Davenport4.39 mg/LApr 2026Human impact clear3 samples147,720
Cedar Rapids Water Department7.29 mg/LMay 2026a high point — runs lowerHealth-study range300 samples142,364
Sioux City Water Supply0.58 mg/LApr 2026Natural background6 samples85,791
Ankeny, City Of5.95 mg/LJun 2026a high point — runs lowerHealth-study range12 samples76,207

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 scatter across the farm counties

Human impact is clear on drinking water served in 59 of Iowa’s 99 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.

IA 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.Black Hawk County — 1 system at 3.00–4.99 mg/L as N; 4 systems at 5.00 mg/L as N or aboveWapello County — 0 systems at 3.00–4.99 mg/L as N; 2 systems at 5.00 mg/L as N or aboveWarren County — 0 systems at 3.00–4.99 mg/L as N; 6 systems at 5.00 mg/L as N or aboveMarshall County — 7 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveDelaware County — 0 systems at 3.00–4.99 mg/L as N; 2 systems at 5.00 mg/L as N or aboveBuchanan County — 2 systems at 3.00–4.99 mg/L as N; 2 systems at 5.00 mg/L as N or aboveBoone County — 1 system at 3.00–4.99 mg/L as N; 7 systems at 5.00 mg/L as N or aboveHardin County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveIda County — 3 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or abovePolk County — 1 system at 3.00–4.99 mg/L as N; 7 systems at 5.00 mg/L as N or aboveMadison County — 1 system at 3.00–4.99 mg/L as N; 3 systems at 5.00 mg/L as N or aboveVan Buren County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveHenry County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveJones County — 1 system at 3.00–4.99 mg/L as N; 2 systems at 5.00 mg/L as N or aboveGreene County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveMitchell County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveMontgomery County — 0 systems at 3.00–4.99 mg/L as N; 2 systems at 5.00 mg/L as N or aboveBremer County — 1 system at 3.00–4.99 mg/L as N; 3 systems at 5.00 mg/L as N or aboveWashington County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or abovePocahontas County — 1 system at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveCrawford County — 1 system at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveGrundy County — 6 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveAudubon County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveLinn County — 3 systems at 3.00–4.99 mg/L as N; 5 systems at 5.00 mg/L as N or aboveSac County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveWoodbury County — 3 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or abovePottawattamie County — 1 system at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveMuscatine County — 1 system at 3.00–4.99 mg/L as N; 3 systems at 5.00 mg/L as N or aboveMills County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveFayette County — 2 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveJasper County — 7 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveDes Moines County — 2 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveStory County — 4 systems at 3.00–4.99 mg/L as N; 3 systems at 5.00 mg/L as N or abovePlymouth County — 2 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveDubuque County — 1 system at 3.00–4.99 mg/L as N; 3 systems at 5.00 mg/L as N or aboveWinneshiek County — 1 system at 3.00–4.99 mg/L as N; 2 systems at 5.00 mg/L as N or aboveClay County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveJohnson County — 1 system at 3.00–4.99 mg/L as N; 3 systems at 5.00 mg/L as N or aboveIowa County — 2 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveBenton County — 0 systems at 3.00–4.99 mg/L as N; 5 systems at 5.00 mg/L as N or aboveScott County — 2 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveHarrison County — 2 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or abovePage County — 4 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveClayton County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveHumboldt County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveSioux County — 3 systems at 3.00–4.99 mg/L as N; 4 systems at 5.00 mg/L as N or aboveDallas County — 3 systems at 3.00–4.99 mg/L as N; 5 systems at 5.00 mg/L as N or aboveCass County — 1 system at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveMonona County — 3 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveJackson County — 2 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveChickasaw County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveGuthrie County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveLee County — 0 systems at 3.00–4.99 mg/L as N; 5 systems at 5.00 mg/L as N or aboveTaylor County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveButler County — 2 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveTama County — 3 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveBuena Vista County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveLyon County — 3 systems at 3.00–4.99 mg/L as N; 5 systems at 5.00 mg/L as N or aboveClinton County — 0 systems at 3.00–4.99 mg/L as N; 1 system 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

Boone leads this layer with 7 reporting systems, followed by Polk, Warren, Benton. Higher results scatter across the farm counties.

Counties with the most systems at or above 3 mg/L as N
County3–4.99≥5Total ≥3
Boone178
Dallas358
Linn358
Lyon358
Marshall718

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 Iowa system

What the statewide pattern says

A tile-drainage pattern, with a karst edge

Iowa's higher nitrate is an agricultural pattern with two pathways: buried tile drains that send it to the rivers, and a karst northeast that sends it straight underground.

Iowa is some of the most intensively farmed ground on earth, and its defining nitrate pathway is the buried tile drain. Tile drainage turned wet prairie into cropland, but it also flushes water and nitrate to the rivers in days — which is why north-central Iowa's cities, drawing from tile-fed rivers, fight nitrate in summer even where nearby wells run low (Dubrovsky and others, 2010).

The second setting is the far northeast: the Paleozoic Plateau, Iowa's share of the Driftless karst, where sinkholes and fractured carbonate give surface nitrogen near-direct access to groundwater. Statewide, the national vulnerability work associates high nitrate with exactly this combination — heavy nitrogen input on permeable or fast-pathway ground (Nolan and Hitt, 2006).

What the public-system map cannot show is the private-well picture, and in Iowa it is studied better than almost anywhere. A USGS–National Cancer Institute model of 34,084 Iowa private wells found well depth dominates risk: mean nitrate runs about 7.7 mg/L in wells shallower than 50 feet versus about 1.0 mg/L below 500 feet, with sinkhole proximity and soil permeability behind depth (Wheeler and others, 2015).

The supported source reading is agricultural — row-crop nitrogen on drained or karst ground — not a certified source at any individual system. Iowa sits at the center of the Corn Belt nitrogen yields that the Mississippi-basin SPARROW model ranks highest in the nation (Robertson and Saad, 2021). And the ground holds decades of old nitrogen, so change arrives slowly, in years rather than seasons.

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 Iowa pattern does—and does not—say

Where does nitrate concentrate in Iowa community water systems?

Boone leads this layer with 7 reporting systems, followed by Polk, Warren, Benton. Higher results scatter across the farm counties.

Why do Iowa cities fight nitrate in rivers while nearby wells run lower?

Tile drainage. Buried field drains flush nitrate to rivers in days, so the tile-fed rivers that central Iowa cities draw from spike in summer, while deeper groundwater receives nitrate slowly or not at all. The karst northeast is the exception: there, nitrate moves straight underground.

What predicts a high Iowa private well?

Depth, above all. In the USGS–NCI model of 34,084 Iowa wells, mean nitrate was about 7.7 mg/L for wells shallower than 50 feet versus about 1.0 mg/L below 500 feet; sinkhole proximity, slope, and soil permeability followed. A certified-lab test is still the only way to know a specific well.

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: 1,060 Iowa 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. Wheeler DC, Nolan BT, Flory AR, DellaValle CT, Ward MH (2015). Modeling groundwater nitrate concentrations in private wells in Iowa. Science of the Total Environment 536:481–488.
  5. Robertson DM, Saad DA (2021). SPARROW Mississippi/Atchafalaya nutrient model. JAWRA 57(3) — Corn Belt nitrogen yields highest in the nation, centered on Iowa and Illinois.
  6. Prior JC (1991). Landforms of Iowa. University of Iowa Press for the Iowa Geological Survey — the landform regions used to place Iowa counties geologically.
  7. Central Iowa Source Water Resource Assessment (2025) — roughly 80% of central Iowa river nitrate is agricultural in origin; noted as reported by the assessment.