Idaho
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Idaho water profile

Nitrate in Idaho community water systems

Idaho's higher nitrate concentrates along the Snake River Plain — the Treasure Valley around Nampa and Caldwell above all, and the Magic Valley dairy country downstream. Nitrate is the most common groundwater contaminant in the state. See what each reporting system measured in the three years from August 9, 2023 to August 9, 2026.

Browse all 767 Idaho systems →

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

100%
of the state’s 767 active community water systems have a current result here
767
systems with a current nitrate result
1,566,791
people served by those reporting systems
7.0%
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 Idaho's systems fall across the five bands

Most systems report below 3 mg/L

Natural background
0.00–0.99 mg/L as N
431 systems · 848,089 served
Human impact likely
1.00–2.99 mg/L as N
220 systems · 515,432 served
Human impact clear
3.00–4.99 mg/L as N
62 systems · 178,802 served
Health-study range
5.00–9.99 mg/L as N
50 systems · 24,073 served
Above the federal limit
10.00 mg/L and above
4 systems · 395 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 54 systems reporting 5 mg/L or more, 32 stayed at or above 5 across the whole three-year range; the other 22 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. 755 systems sampled their own water; 12 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
Eaton Mobile Home Court32.60 mg/LMay 2026a high point — runs lowerAbove the federal limit4 samples94
Meadow Lark Court Llc16.94 mg/LOct 2024a high point — runs lowerAbove the federal limit11 samples45
Drake Subd12.20 mg/LDec 2025Above the federal limit18 samples150
Whitewater Subd10.74 mg/LApr 2026a high point — runs lowerAbove the federal limit12 samples106
D And S Purple Sage Ranchettes9.91 mg/LApr 2026a high point — runs lowerHealth-study range24 samples70
Kimpton Acres Third Subd9.80 mg/LApr 2026Health-study range24 samples88
Ferdinand City Of8.87 mg/LJun 2026Health-study range27 samples133
Purple Sage Community8.40 mg/LJan 2026a high point — runs lowerHealth-study range14 samples98
Largest systems
SystemMost recent resultBandBased onPeople served
Veolia Water Idaho0.10 mg/LJun 2026Natural background183 samples264,978
Meridian Water Dept0.80 mg/LJun 2026Natural background66 samples147,340
Nampa City Of0.50 mg/LMay 2026Natural background39 samples100,200
Caldwell City Of2.30 mg/LApr 2026Human impact likely42 samples74,000
Idaho Falls City Of1.53 mg/LSep 2025Human impact likely51 samples69,450

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 concentrate in the Treasure and Magic valleys

Human impact is clear on drinking water served in 28 of Idaho’s 44 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.

ID 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.Gem County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveIdaho County — 1 system at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveCassia County — 1 system at 3.00–4.99 mg/L as N; 2 systems at 5.00 mg/L as N or aboveGooding County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveOneida County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveBoise County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveBonneville County — 3 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveKootenai County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveElmore County — 3 systems at 3.00–4.99 mg/L as N; 8 systems at 5.00 mg/L as N or aboveFremont County — 1 system at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveBannock County — 3 systems at 3.00–4.99 mg/L as N; 2 systems at 5.00 mg/L as N or aboveTeton County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or abovePayette County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or abovePower County — 2 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveLewis County — 2 systems at 3.00–4.99 mg/L as N; 2 systems at 5.00 mg/L as N or aboveNez Perce County — 3 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveTwin Falls County — 4 systems at 3.00–4.99 mg/L as N; 5 systems at 5.00 mg/L as N or aboveAdams County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveBear Lake County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveFranklin County — 1 system at 3.00–4.99 mg/L as N; 3 systems at 5.00 mg/L as N or aboveLatah County — 3 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveOwyhee County — 1 system at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveMadison County — 2 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveBingham County — 2 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveWashington County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveAda County — 11 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveCanyon County — 11 systems at 3.00–4.99 mg/L as N; 22 systems at 5.00 mg/L as N or aboveCaribou County — 1 system 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

Canyon leads this layer with 22 reporting systems, followed by Elmore, Twin Falls, Franklin. Higher results concentrate in the Treasure and Magic valleys.

Counties with the most systems at or above 3 mg/L as N
County3–4.99≥5Total ≥3
Canyon112233
Ada11112
Elmore3811
Twin Falls459
Bannock325

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 Idaho system

What the statewide pattern says

A Snake River Plain pattern

Idaho's higher nitrate tracks the Snake River Plain aquifer system: shallow, irrigation-recharged sediments and fractured basalt under some of the heaviest dairy and irrigated-crop country in the West.

The Treasure Valley — Canyon County and its neighbors — leads the public-system map, and it sits in a setting the state already watches: Idaho DEQ's nitrate priority areas include northeast Canyon County, where septic density adds to the agricultural signal over shallow aquifers. The Idaho Geological Survey is currently modeling septic nitrate loading there to guide development rules (Idaho DEQ and Idaho Geological Survey programs).

Downstream, the Magic Valley is the dairy heartland, and its shallow fringe runs hot. The eastern Snake River Plain aquifer is famously productive, but where it thins and pinches out toward the Snake River, shallow groundwater dominates: USGS modeling links that geometry to the valley's elevated nitrate (Rupert and others, 2014). Idaho DEQ's worst-ranked nitrate priority area, Marsh Creek, averaged 6.8 mg/L with a maximum of 40 mg/L in the 2020 assessment, and regional trend work finds nitrate still rising in parts of the mid-Snake (Skinner, 2022).

The supported source reading is agricultural — manure-heavy in the Magic Valley dairy country, fertilizer-and-septic in the Treasure Valley — not a certified source at any individual system. Regionally the basalt aquifer keeps most of its deep water low — about 3 percent of Snake River Plain wells exceeded the limit in USGS's assessment — so the pattern is a shallow-fringe problem more than a whole-aquifer 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 Idaho pattern does—and does not—say

Where does nitrate concentrate in Idaho community water systems?

Canyon leads this layer with 22 reporting systems, followed by Elmore, Twin Falls, Franklin. Higher results concentrate in the Treasure and Magic valleys.

Why is the deep Snake River Plain aquifer mostly clean while wells still run high?

Geometry. The regional basalt aquifer is deep and well-flushed — only about 3 percent of its wells exceeded the federal limit in USGS's assessment — but where it thins and pinches out toward the Snake River, shallow, recently recharged water dominates, and that is where nitrate concentrates. Depth and position matter more than the aquifer's name.

Can this page say the source is agriculture?

At the zone level, yes — carefully: manure-heavy in the Magic Valley dairy country, fertilizer and septic mixed in the Treasure Valley. 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: 767 Idaho 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. Rupert MG, Hunt CD, Skinner KD, Frans LM, Mahler BJ (2014). Groundwater quality in the Columbia Plateau and Snake River Plain basin-fill and basaltic-rock aquifers. USGS Circular 1359.
  5. Skinner KD (2022). Trends in groundwater levels, and orthophosphate and nitrate concentrations in the Middle Snake River region, south-central Idaho. USGS Scientific Investigations Report 2022-5060.
  6. Idaho Department of Environmental Quality (2020). Nitrate Priority Area assessment — 35 ranked areas; Marsh Creek averaged 6.8 mg/L (max 40 mg/L); nitrate identified as Idaho’s most common groundwater contaminant.
  7. Idaho Geological Survey — Groundwater Nitrate-Loading Modeling Project, Treasure Valley (2023–2026), under contract to Idaho DEQ.