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Colorado water profile

Nitrate in Colorado community water systems

Colorado's nitrate map is the High Plains made visible: the elevated systems run down the South Platte corridor and across the eastern irrigation counties, where some of the nation's most-cited nitrate science was written. See the pattern and what each reporting system measured in the three years from August 9, 2023 to August 9, 2026.

Browse all 1,033 Colorado systems →

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

98%
of the state’s 1,056 active community water systems have a current result here
1,033
systems with a current nitrate result
7,148,969
people served by those reporting systems
4.9%
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 Colorado's systems fall across the five bands

Most systems report below 3 mg/L

Natural background
0.00–0.99 mg/L as N
827 systems · 6,336,683 served
Human impact likely
1.00–2.99 mg/L as N
116 systems · 466,810 served
Human impact clear
3.00–4.99 mg/L as N
39 systems · 159,953 served
Health-study range
5.00–9.99 mg/L as N
50 systems · 184,873 served
Above the federal limit
10.00 mg/L and above
1 system · 650 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 51 systems reporting 5 mg/L or more, 16 stayed at or above 5 across the whole three-year range; the other 35 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. 739 systems sampled their own water; 294 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
Walsh Town Of11.10 mg/LApr 2026Above the federal limit16 samples650
Genoa Town Of9.90 mg/LJan 2026Health-study range9 samples153
Rolling Plains Estate9.40 mg/LMay 2026Health-study range13 samples40
Burlington City Of9.20 mg/LJun 2026a high point — runs lowerHealth-study range70 samples3,720
Flagler Town Of9.00 mg/LApr 2026Health-study range12 samples2,160
Haswell Town Of7.90 mg/LMay 2026a high point — runs lowerHealth-study range35 samples55
Seibert Town Of7.80 mg/LApr 2026Health-study range12 samples296
Peaks Shadow Llc7.70 mg/LFeb 2026Health-study range10 samples67
Largest systems
SystemMost recent resultBandBased onPeople served
Denver Water Board0.08 mg/LMar 2026Natural background86 samples1,287,000
Aurora City Of0.41 mg/LMay 2026Natural background62 samples533,407
Colorado Springs Utilities0.00 mg/LJul 2025Natural background8 samples464,111
Thornton City Of1.02 mg/LSep 2025Human impact likely6 samples226,465
Westminster City Of0.05 mg/LMay 2025Natural background4 samples202,078

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

The South Platte corridor and the eastern plains

Human impact is clear on drinking water served in 31 of Colorado’s 64 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.

CO 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.Washington County — 1 system at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveGarfield County — 3 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveRio Grande County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveMorgan County — 0 systems at 3.00–4.99 mg/L as N; 2 systems at 5.00 mg/L as N or aboveElbert County — 2 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveOtero County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveTeller County — 0 systems at 3.00–4.99 mg/L as N; 4 systems at 5.00 mg/L as N or abovePhillips County — 1 system at 3.00–4.99 mg/L as N; 2 systems at 5.00 mg/L as N or aboveYuma County — 2 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveBaca County — 1 system at 3.00–4.99 mg/L as N; 2 systems at 5.00 mg/L as N or aboveArapahoe County — 1 system at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveJefferson County — 3 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveSummit County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveWeld County — 3 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveLas Animas County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveBoulder County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveLarimer County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveCrowley County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveEl Paso County — 3 systems at 3.00–4.99 mg/L as N; 8 systems at 5.00 mg/L as N or aboveHuerfano County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveCheyenne County — 2 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or abovePitkin County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveKit Carson County — 1 system at 3.00–4.99 mg/L as N; 5 systems at 5.00 mg/L as N or aboveClear Creek County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveKiowa County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or abovePark County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveLake County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveLincoln County — 1 system at 3.00–4.99 mg/L as N; 2 systems at 5.00 mg/L as N or aboveAdams County — 1 system at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveLogan County — 4 systems at 3.00–4.99 mg/L as N; 2 systems at 5.00 mg/L as N or aboveSedgwick County — 0 systems at 3.00–4.99 mg/L as N; 3 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

El Paso leads this layer with 8 reporting systems, followed by Kit Carson, Teller, Sedgwick. The South Platte corridor and the eastern plains. Coverage note: the map places 76% of Colorado’s reporting systems. All 246 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
El Paso3811
Kit Carson156
Logan426
Garfield314
Jefferson314

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 76% of Colorado’s reporting systems. All 246 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 Colorado system

What the statewide pattern says

Irrigated plains, oxidizing aquifers, and nitrate that stays nitrate

Colorado's elevated systems concentrate in the South Platte alluvial corridor — Weld, Logan, Sedgwick, Phillips — and the High Plains irrigation counties of the east, with a Front Range cluster in El Paso and Jefferson on alluvial and Denver Basin aquifers.

Colorado's 78 mapped systems above the natural-background band draw two features: the South Platte River corridor from Weld through Logan, Sedgwick and Phillips, and the High Plains irrigation counties — Kit Carson, Cheyenne, Lincoln, Baca — plus a Front Range cluster in El Paso and Jefferson and a mountain scatter led by Teller. Nearly 5 percent of the state's reporting systems sit at or above 3.00 mg/L.

The South Platte alluvial aquifer is where American nitrate science grew up. USGS work near Greeley documented nitrogen loading from irrigated crops and poultry farms directly into the alluvium (Gaggiani, USGS), and McMahon and Böhlke's studies of denitrification and mixing in the stream–aquifer system became the national reference for how nitrate moves, mixes and occasionally breaks down along an irrigation river (Colorado Geological Survey bibliography).

The eastern plains' vulnerability is quantified. USGS modeled the High Plains aquifer's recently recharged groundwater from 336 wells — median nitrate 3.82 mg/L, 48 percent of samples above 4 mg/L, 13 percent above the 10 mg/L federal limit — and found vulnerability tracks the percentage of agricultural land, shallow depth to water, and low clay and organic matter in the unsaturated zone; the aquifer's oxidizing conditions give denitrification little chance (USGS SIR 2006-5050).

The honest gap: the Front Range and mountain clusters — El Paso, Teller, Jefferson — mix alluvial, Denver Basin and fractured-bedrock settings with septic growth, but dedicated county nitrate studies for them are thin; this page reads their setting only. The supported source reading is irrigated-agriculture nitrogen on the South Platte alluvium and the High Plains; mixed and setting-only along the Front Range — not a certified source at any individual system (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 Colorado pattern does—and does not—say

Where does nitrate concentrate in Colorado community water systems?

El Paso leads this layer with 8 reporting systems, followed by Kit Carson, Teller, Sedgwick. The South Platte corridor and the eastern plains.

Why is the South Platte corridor so prominent for nitrate?

A century of irrigated agriculture on a shallow, oxidizing alluvial aquifer. Fertilizer and manure nitrogen reach the water table with little in the unsaturated zone to stop them, and the same USGS studies that defined the science — Greeley-area loading studies and McMahon and Böhlke's denitrification work — were written on this river.

Should a Colorado private well be tested for nitrate?

Yes, especially in the eastern irrigation counties and the South Platte corridor, where USGS measured a 3.82 mg/L median and 13 percent of sampled wells over the federal limit in recently recharged groundwater. Front Range bedrock wells add uranium and arsenic to the panel's case.

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: 1,033 Colorado 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. Gurdak JJ, and others (2007). Vulnerability of Recently Recharged Ground Water in the High Plains Aquifer to Nitrate Contamination. USGS SIR 2006-5050 — 336 wells: median 3.82 mg/L, 48% >4 mg/L, 13% >10 mg/L; vulnerability tracks agricultural land, shallow water table, low clay and organic matter.
  5. Colorado Geological Survey. Colorado Groundwater Atlas bibliography — canonical South Platte nitrate literature: Gaggiani, Nitrogen, Sulfate, Chloride and Manganese in Ground Water in the Alluvial Deposits of the South Platte River Valley near Greeley (USGS); McMahon and Böhlke, Denitrification and Mixing in a Stream-Aquifer System (1996); McMahon, Böhlke and Litke, Fate of Nitrate in the South Platte River Alluvial Aquifer System (1995).