Well Water in Erie, Colorado

Weld & Boulder County · Population ~38,000 · Aquifer: Municipal C-BT surface water; Dawson / Denver Basin + alluvial wells on the rural fringe

Hardness: Hard in Denver Basin bedrock wells; municipal supply moderated by treatment

Erie's Municipal Water Is Colorado–Big Thompson Surface Water

The Town of Erie Water Resources Department provides 100 percent surface water. The primary source is Colorado–Big Thompson (C-BT) Project water, diverted from the western slope and delivered by pipeline from Carter Lake in Berthoud to Erie's Lynn R. Morgan Water Treatment Facility. Secondary sources include Windy Gap deliveries and the South Boulder Canyon Ditch, which fills Erie's reservoirs from Gross Reservoir, with storage in Erie Lake and Thomas Reservoir. The incorporated town is essentially all municipal surface water; no authoritative municipal-versus-well percentage is published, but wells are a rural-fringe phenomenon.

Rural Wells on the Western Denver Basin Edge

Erie sits at the western edge of the Denver Basin, where the basin's bedrock aquifers meet the Front Range. Rural wells in and around Erie draw from the shallow alluvial aquifer along the Coal Creek and South Boulder Creek drainages, and from the Denver Basin bedrock system — principally the uppermost Dawson aquifer, which is shallow and near outcrop along this western edge, with the Denver, Arapahoe, and Laramie–Fox Hills aquifers available at depth. The Erie area is the historic Denver Basin coal-mining district (toward Marshall), so the Laramie–Fox Hills is locally relevant.

For Weld County wells, a USGS model estimates roughly a 7 percent probability of a well exceeding the 10 µg/L arsenic standard, with nitrate the other primary concern in this agricultural area. Denver Basin bedrock groundwater also carries naturally occurring uranium, radium, and radon, and total dissolved solids rise sharply with depth — the USGS measured TDS from under 100 mg/L in the shallow Dawson aquifer to around 2,000 mg/L in the Laramie Formation.

Municipal Water Quality and the PFAS Note

Erie's 2025 Drinking Water Quality Report (calendar-year 2024 data) showed no health-based violations. Notable detections were well below limits: nitrate 0.08 ppm (limit 10), combined uranium 1 ppb (limit 30), fluoride 0.82 ppm (limit 4), and lead at the 90th percentile of 0.0052 ppb (action level 15).

On PFAS: in March 2023 the Town reported no detectable PFAS in Erie's finished drinking water, but a small trace of 4.5 ppt in raw water at Erie Lake — against the then-new 4 ppt EPA limit for PFOA/PFOS. Erie's plant uses activated-carbon filtration that reduces PFAS, and the Town reported it remained in compliance. The important distinction is raw versus finished water: the trace was in the source reservoir, not the tap.

A Future-Supply Wrinkle: Chimney Hollow

Erie's future supply depends in part on Northern Water's Chimney Hollow Reservoir (part of the Windy Gap Firming project) and the NISP/Glade project; Erie has committed tens of millions of dollars to each. Filling of the newly built Chimney Hollow was delayed after uranium was found leaching from the granite dam rock in 2025–26 — a reminder, close to home, that the Front Range granite naturally carries uranium and its decay products.

What Erie Residents Should Know

If you're on Town of Erie water (the incorporated town): your water is treated C-BT surface water meeting all standards, with no finished-water PFAS detected.

If you're on a private well on the rural Weld/Boulder fringe: test for arsenic, nitrate, radionuclides (uranium, radium, radon), bacteria, hardness, and TDS — and expect deeper bedrock wells to trend harder and more mineralized. See our testing guide.