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Oregon water profile

Nitrate in Oregon community water systems

Oregon's higher nitrate gathers in two settings: the Willamette Valley's shallow alluvium and the irrigated northeast, home to the Lower Umatilla Basin — one of the longest-documented groundwater nitrate problems in the West. See what each reporting system measured in the three years from August 9, 2023 to August 9, 2026.

Browse all 932 Oregon systems →

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

100%
of the state’s 937 active community water systems have a current result here
932
systems with a current nitrate result
3,747,065
people served by those reporting systems
2.7%
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 Oregon's systems fall across the five bands

Most systems report below 3 mg/L

Natural background
0.00–0.99 mg/L as N
675 systems · 3,405,267 served
Human impact likely
1.00–2.99 mg/L as N
177 systems · 210,642 served
Human impact clear
3.00–4.99 mg/L as N
55 systems · 66,744 served
Health-study range
5.00–9.99 mg/L as N
23 systems · 64,255 served
Above the federal limit
10.00 mg/L and above
2 systems · 157 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 25 systems reporting 5 mg/L or more, 11 stayed at or above 5 across the whole three-year range; the other 14 reached it only on a high sample and otherwise ran lower.

Most recent reading Jun 2026; the typical system was last tested around Nov 2025. 851 systems sampled their own water; 81 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
Golf Mhp13.90 mg/LJun 2026a high point — runs lowerAbove the federal limit28 samples60
Tooley Water District10.80 mg/LMar 2026a high point — runs lowerAbove the federal limit43 samples97
Fischers Place Mhp9.87 mg/LMay 2026a high point — runs lowerHealth-study range3 samples130
Sunridge Water Inc9.40 mg/LApr 2026Health-study range18 samples200
Monmouth, City Of8.72 mg/LMay 2026a high point — runs lowerHealth-study range12 samples11,651
Harwoods Mobile Manor8.37 mg/LJan 2026Health-study range4 samples65
Mint Acres Water Co-Op8.32 mg/LApr 2026Health-study range6 samples35
Colorado Lake Coop8.29 mg/LApr 2026Health-study range10 samples80
Largest systems
SystemMost recent resultBandBased onPeople served
Portland Water Bureau0.11 mg/LJul 2025Natural background5 samples666,200
Tualatin Valley Water District0.61 mg/LSep 2023Natural background*1 sample224,600
Salem Public Works0.03 mg/LApr 2026Natural background23 samples199,820
Eugene Water & Electric Board0.03 mg/LMay 2026Natural background12 samples176,000
Medford Water Commission0.10 mg/LAug 2025Natural background2 samples106,068

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 Willamette Valley and the irrigated northeast

Human impact is clear on drinking water served in 22 of Oregon’s 36 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.

OR 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.Gilliam County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveJosephine County — 3 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveLinn County — 7 systems at 3.00–4.99 mg/L as N; 4 systems at 5.00 mg/L as N or aboveMarion County — 10 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveColumbia County — 4 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveHarney County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveMorrow County — 1 system at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveLane County — 5 systems at 3.00–4.99 mg/L as N; 2 systems at 5.00 mg/L as N or aboveYamhill County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveDeschutes County — 2 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveClackamas County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or abovePolk County — 1 system at 3.00–4.99 mg/L as N; 2 systems at 5.00 mg/L as N or aboveMultnomah County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveWallowa County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveMalheur County — 1 system at 3.00–4.99 mg/L as N; 4 systems at 5.00 mg/L as N or aboveWasco County — 1 system at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveHood River County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveTillamook County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveCrook County — 2 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveUmatilla County — 6 systems at 3.00–4.99 mg/L as N; 3 systems at 5.00 mg/L as N or aboveSherman County — 1 system at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveJackson County — 5 systems at 3.00–4.99 mg/L as N; 2 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

Linn leads this layer with 4 reporting systems, followed by Malheur, Umatilla, Jackson. Higher results gather in the Willamette Valley and the irrigated northeast.

Counties with the most systems at or above 3 mg/L as N
County3–4.99≥5Total ≥3
Linn7411
Marion10111
Umatilla639
Jackson527
Lane527

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 Oregon system

What the statewide pattern says

Three groundwater management areas tell the story

Oregon has declared three groundwater management areas for nitrate — the Lower Umatilla Basin, the Southern Willamette Valley, and Northern Malheur County — and the public-system map tracks all three.

The Lower Umatilla Basin is the marquee case. Oregon declared it a Groundwater Management Area in 1990 after nitrate in many wells exceeded the state's 7 mg/L trigger, and the technical study behind the declaration named five sources: irrigated agriculture, confined animal feeding operations, land-applied food-processing water, septic systems, and the Umatilla Chemical Depot's washout lagoons (Grondin and others, 1995, Oregon DEQ). Three decades later the basin remains contaminated; Morrow County declared a groundwater emergency in 2022 after local testing found widespread domestic-well exceedances.

The state's two other designated areas match the rest of the map. The Southern Willamette Valley GWMA covers the shallow alluvial aquifer of Linn and Lane counties — the same counties that lead this page's table — and Northern Malheur County, on the Idaho border, shares the irrigated Snake River plain setting. Oregon's declarations rest on the same recipe the national work describes: nitrogen loading over permeable, oxic aquifers (Nolan and Hitt, 2006).

The supported source reading is agricultural with documented sub-sources — fertilizer on irrigated fields, CAFO manure, and food-processing wastewater, with septic in rural-residential pockets. Few states have a source list this explicitly established; the caveat is that it applies to the designated basins, not to every system on the map (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 Oregon pattern does—and does not—say

Where does nitrate concentrate in Oregon community water systems?

Linn leads this layer with 4 reporting systems, followed by Malheur, Umatilla, Jackson. Higher results gather in the Willamette Valley and the irrigated northeast.

What is a groundwater management area?

Oregon's Groundwater Protection Act requires the state to declare one where nonpoint-source contamination pushes groundwater past a trigger level — for nitrate, 7 mg/L. Oregon has three: the Lower Umatilla Basin (1990), Northern Malheur County (1989), and the Southern Willamette Valley. The Lower Umatilla's 1995 technical study named five nitrate sources explicitly, from irrigated agriculture to septic systems.

Can this page say the source is agriculture?

In the designated basins, yes — and more specifically than most states can: irrigated agriculture, CAFO manure, and food-processing wastewater are on the state's own source list, alongside septic systems. Outside the designated basins, treat the reading as zone-level only.

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: 932 Oregon 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. Grondin GH, and others (1995). Hydrogeology, groundwater chemistry, and land use in the Lower Umatilla Basin Groundwater Management Area. Oregon Department of Environmental Quality — the technical study naming the basin’s five nitrate sources.
  5. Oregon Department of Environmental Quality — Groundwater Management Area program (Lower Umatilla Basin, declared 1990; Northern Malheur County; Southern Willamette Valley) — designations under the Groundwater Protection Act of 1989.
  6. Morrow County, Oregon (2022) — county groundwater emergency declaration following domestic-well nitrate testing; noted as a governmental action, with state testing by the Oregon Health Authority continuing since 2023.