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Ohio water profile

Nitrate in Ohio community water systems

Ohio's signature nitrate-and-nutrient story is surface water — the Maumee River and the algal blooms of western Lake Erie — while groundwater stays moderate outside a few vulnerable pockets. See where higher public-system results sit and what each reporting system measured in the three years from August 9, 2023 to August 9, 2026.

Browse all 1,112 Ohio systems →

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

99%
of the state’s 1,127 active community water systems have a current result here
1,112
systems with a current nitrate result
10,247,056
people served by those reporting systems
2.2%
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 Ohio's systems fall across the five bands

Most systems report below 3 mg/L

Natural background
0.00–0.99 mg/L as N
890 systems · 5,843,016 served
Human impact likely
1.00–2.99 mg/L as N
156 systems · 2,635,294 served
Human impact clear
3.00–4.99 mg/L as N
42 systems · 1,674,943 served
Health-study range
5.00–9.99 mg/L as N
24 systems · 93,803 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 24 systems reporting 5 mg/L or more, 1 stayed at or above 5 across the whole three-year range; the other 23 reached it only on a high sample and otherwise ran lower.

Most recent reading Jun 2026; the typical system was last tested around Mar 2026. 856 systems sampled their own water; 256 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
Delphos City7.56 mg/LJun 2026a high point — runs lowerHealth-study range35 samples7,101
Dawsons Mobile Home Park Pws6.85 mg/LFeb 2026Health-study range3 samples51
Laurelville, Vlg Of6.82 mg/LJun 2026a high point — runs lowerHealth-study range35 samples586
Greenville City Pws6.51 mg/LJun 2026a high point — runs lowerHealth-study range35 samples13,227
Carey Village Pws6.34 mg/LJun 2026Health-study range12 samples3,674
Liberty Center Village6.21 mg/LJun 2026a high point — runs lowerHealth-study rangeinherited from supplier1,350
Waterville City6.21 mg/LJun 2026a high point — runs lowerHealth-study rangeinherited from supplier6,500
Bowling Green City6.21 mg/LJun 2026a high point — runs lowerHealth-study range36 samples31,578
Largest systems
SystemMost recent resultBandBased onPeople served
Cleveland Public Water System0.41 mg/LJun 2026Natural background144 samples1,308,955
Columbus Public Water System4.70 mg/LJun 2026a high point — runs lowerHuman impact clear75 samples1,305,946
Cincinnati Public Water System1.01 mg/LJun 2026Human impact likely40 samples750,200
Toledo City Of1.35 mg/LJun 2026Human impact likely35 samples360,000
Akron City Pws0.04 mg/LJun 2026Natural background39 samples280,000

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 sit in the farmed northwest and the buried valleys

Human impact is clear on drinking water served in 33 of Ohio’s 88 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.

OH 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.Knox 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; 0 systems at 5.00 mg/L as N or aboveShelby County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveVan Wert County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveLicking County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveDarke County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveSandusky County — 2 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveHocking County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveLucas County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveMeigs County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveHuron County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveRichland County — 4 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveBelmont County — 1 system at 3.00–4.99 mg/L as N; 2 systems at 5.00 mg/L as N or aboveWood County — 0 systems at 3.00–4.99 mg/L as N; 6 systems at 5.00 mg/L as N or aboveButler County — 2 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveWashington County — 4 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveMontgomery County — 1 system at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or abovePreble County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveClark County — 1 system at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveSeneca County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or abovePike County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveLawrence County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveClermont County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveCuyahoga County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveFranklin County — 11 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveClinton County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveAllen 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; 6 systems at 5.00 mg/L as N or aboveMiami County — 2 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveWyandot County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveChampaign County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveMahoning County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveMonroe 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

Henry leads this layer with 6 reporting systems, followed by Wood, Belmont, Allen. Higher results sit in the farmed northwest and the buried valleys.

Counties with the most systems at or above 3 mg/L as N
County3–4.99≥5Total ≥3
Franklin11011
Henry066
Wood066
Richland404
Washington404

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 Ohio system

What the statewide pattern says

A surface-water state, with groundwater pockets

Ohio's farm nutrients run to the rivers — the Maumee to western Lake Erie — while groundwater nitrate stays moderate except in shallow buried-valley aquifers and the farmed carbonate belt of the west.

Glaciated northwestern Ohio is intensively farmed and tile-drained, and its nutrients run to surface water: the Maumee River basin draining to western Lake Erie, where nitrogen and phosphorus feed the summer algal blooms that have twice threatened Toledo's drinking water. The tile drains that route nitrate to the rivers keep groundwater moderate across much of the state (Robertson and Saad, 2021).

Groundwater runs higher in permeable pockets: the buried-valley aquifers — sand and gravel filling old bedrock valleys, like the Great Miami and the Scioto — which are high-yield but shallow and exposed, and the shallow carbonate bedrock of western Ohio under farmland (Nolan and Hitt, 2006). The map reflects it: Henry and Wood counties in the northwestern carbonate farm belt and Franklin County on the Scioto buried valley carry the most higher-band systems.

Unglaciated eastern Ohio is a different, generally lower-nitrate setting (Dubrovsky and others, 2010). The supported source reading is agricultural — farm nitrogen on shallow carbonate or buried-valley aquifers — not a certified source at any individual system.

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 Ohio pattern does—and does not—say

Where does nitrate concentrate in Ohio community water systems?

Henry leads this layer with 6 reporting systems, followed by Wood, Belmont, Allen. Higher results sit in the farmed northwest and the buried valleys.

If Ohio's nitrate goes to the rivers, why do some wells run high?

Because the routing depends on the aquifer. Tile-drained till plains send nitrate to streams, but shallow buried-valley sand-and-gravel and western carbonate bedrock are permeable and exposed, so wells there can run elevated under farmland even while the state's headline problem plays out in Lake Erie.

Can this page say the source is agriculture?

At the zone level, yes — carefully: farm nitrogen on shallow carbonate or buried-valley aquifers. The evidence does not certify a source at each 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: 1,112 Ohio 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. Robertson DM, Saad DA (2021). SPARROW Mississippi/Atchafalaya nutrient model. JAWRA 57(3) — the tile-drained surface-water pathway to the Gulf and Lake Erie basins.