Missouri
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Missouri water profile

Nitrate in Missouri community water systems

Missouri is a quiet nitrate state: nearly all of its community water systems report below 3 mg/L, and the few higher readings scatter thinly. The geological reason to watch is the Ozark karst. See the pattern and what each reporting system measured in the three years from August 9, 2023 to August 9, 2026.

Browse all 1,420 Missouri systems →

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

99%
of the state’s 1,431 active community water systems have a current result here
1,420
systems with a current nitrate result
5,631,490
people served by those reporting systems
0.6%
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 Missouri's systems fall across the five bands

Most systems report below 3 mg/L

Natural background
0.00–0.99 mg/L as N
1,305 systems · 4,057,590 served
Human impact likely
1.00–2.99 mg/L as N
93 systems · 1,519,030 served
Human impact clear
3.00–4.99 mg/L as N
13 systems · 39,708 served
Health-study range
5.00–9.99 mg/L as N
9 systems · 15,162 served
Above the federal limit
10.00 mg/L and above
0 systems · 0 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 9 systems reporting 5 mg/L or more, 5 stayed at or above 5 across the whole three-year range; the other 4 reached it only on a high sample and otherwise ran lower.

Most recent reading Jun 2026; the typical system was last tested around Dec 2025. 1,119 systems sampled their own water; 301 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
Conway Pws8.86 mg/LApr 2026a high point — runs lowerHealth-study range17 samples788
Wayland Pws6.79 mg/LApr 2026Health-study rangeinherited from supplier420
Wyaconda Pws6.79 mg/LApr 2026Health-study rangeinherited from supplier209
Clark County Cons Pwsd 16.79 mg/LApr 2026Health-study range11 samples7,140
Marion County Pwsd 16.79 mg/LApr 2026a high point — runs lowerHealth-study rangeinherited from supplier4,900
New Hamburg Central5.54 mg/LNov 2025Health-study range5 samples45
Osborn Pws5.48 mg/LJul 2024Health-study range4 samples405
Maitland Pws5.16 mg/LApr 2026Health-study range11 samples155
Largest systems
SystemMost recent resultBandBased onPeople served
Mo American St Louis St Charles Counties1.28 mg/LApr 2026Human impact likely5 samples1,111,000
Kansas City Pws0.93 mg/LMay 2025Natural background2 samples513,800
St Louis City Pws0.58 mg/LMay 2025Natural background4 samples304,709
Springfield Pws0.98 mg/LMar 2026Natural background9 samples210,898
City Of Columbia Utilities0.04 mg/LJan 2026Natural background3 samples126,254

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 thin scatter of higher readings

Human impact is clear on drinking water served in 14 of Missouri’s 115 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.

MO 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.Laclede County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveNewton County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveMarion County — 1 system at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveDeKalb County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveFranklin County — 2 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveMiller County — 2 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or abovePike County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveScott County — 1 system at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveClark County — 0 systems at 3.00–4.99 mg/L as N; 3 systems at 5.00 mg/L as N or aboveNodaway County — 2 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveMorgan County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveTaney County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveHolt County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveCape Girardeau County — 2 systems at 3.00–4.99 mg/L as N; 0 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

Clark leads this layer with 3 reporting systems, followed by DeKalb, Holt, Laclede. A thin scatter of higher readings. Coverage note: the map places 95% of Missouri’s reporting systems. All 70 of the rest buy their water and carry their supplier’s result, which was measured at the supplier’s source — shading their own county would put the reading in the wrong place. They are counted in the figures above.

Counties with the most systems at or above 3 mg/L as N
County3–4.99≥5Total ≥3
Clark033
Cape Girardeau202
Franklin202
Marion112
Miller202

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. Coverage note: the map places 95% of Missouri’s reporting systems. All 70 of the rest buy their water and carry their supplier’s result, which was measured at the supplier’s source — shading their own county would put the reading in the wrong place. They are counted in the figures above.

Find a specific Missouri system

What the statewide pattern says

Mostly low, on karst that deserves respect

Missouri's public systems run low — but the Ozark karst beneath the southern half of the state is exactly the terrain where surface nitrogen can reach groundwater fast, and private wells there are the population to watch.

The baseline numbers are low, and USGS measured them directly. Across the Ozark Plateaus, median nitrate ran about 0.3 mg/L in Ozark-aquifer wells and 0.5 mg/L in its springs; the shallower Springfield Plateau aquifer ran higher at about 1.0 mg/L in wells and 2.6 mg/L in springs — and confined parts of both aquifers ran lower than unconfined parts (USGS Circular 1158).

Public-supply wells check out clean at the state level: in a USGS–state survey of southern Missouri public-supply wells, no measured constituent exceeded Missouri’s drinking-water standards, with the bootheel differing chemically from the Ozark groups (USGS Water-Resources Investigations Report 00-4260).

What the low public-system numbers do not cover is the karst hazard itself. Karst features across the Springfield and Salem Plateaus connect surface water and groundwater directly, and Ozark spring water shows it: nitrate in springs of the upper White River basin has been measured at 13 times the level of the more forested Current River basin, attributed to greater population and livestock density (USGS Professional Paper 1414-D). So the honest Missouri reading is: low typical values on vulnerable terrain.

The supported source reading is agricultural and on-site wastewater nitrogen where the karst is unconfined — not a certified source at any individual system, and in most of the state a potential pattern rather than a measured public-system one (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 Missouri pattern does—and does not—say

Where does nitrate concentrate in Missouri community water systems?

Clark leads this layer with 3 reporting systems, followed by DeKalb, Holt, Laclede. A thin scatter of higher readings.

Missouri's systems test low — why does the page still flag the Ozarks?

Because the aquifer setting, not the average, sets the risk. The Ozark karst connects surface and groundwater directly, and USGS measured springs and shallow wells running several times higher than deep public wells — the exact setting of unregulated private wells, which the public-system data never samples.

Is confined or unconfined the safer setting in Missouri?

Confined. USGS found nitrate in the confined parts of the Ozark and Springfield Plateau aquifers lower than in the unconfined parts, where land-use differences reach the water table. Well depth and a protective confining layer are the two best structural protections.

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: 1,420 Missouri 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. USGS (1998). Water Quality in the Ozark Plateaus. Circular 1158 — median nitrate about 0.3 mg/L in Ozark-aquifer wells, 2.6 mg/L in Springfield Plateau springs; confined aquifers lower.
  5. USGS (2001). Microbiological and chemical quality of ground water used as a source of public supply in southern Missouri — Phase II. Water-Resources Investigations Report 00-4260 — no constituent exceeded state drinking-water standards.
  6. Imes JL, Emmett LF (1994). Geohydrology of the Ozark Plateaus aquifer system. USGS Professional Paper 1414-D — upper White River basin spring nitrate 13× the Current River basin, attributed to population and livestock density.