Well Water in Arvada, Colorado

Jefferson County · Population ~124,000 · Aquifer: Municipal mountain surface water; Denver Basin + fractured-rock wells on the western foothills fringe

Hardness: Soft (municipal, ~43–65 ppm); harder in Denver Basin groundwater

Arvada's Water Is Mountain Surface Water

The City of Arvada is the primary water utility, delivering over 6.2 billion gallons annually through 531 miles of water lines, two treatment plants, nine tanks, and six pump stations. Its two surface sources are Denver Water's North System — the primary year-round supply, delivered from Denver Water's Ralston Reservoir, itself filled by snowmelt from the Fraser River and South Boulder Creek basins via Gross Reservoir — and Clear Creek, which provides the remaining roughly 25 percent, diverted through canals to Arvada Reservoir. The Ralston Water Treatment Plant runs year-round and the Arvada Water Treatment Plant handles peak season.

Some areas within the city are served by other districts — Denver Water directly in parts of the city, and Ralston Valley Water & Sanitation District in northwest Arvada, which purchases all of its treated water from the City of Arvada. The built-out city is essentially all municipal surface water.

Foothills Wells: Radon and the Western Denver Basin

Private wells concentrate on the western foothills edge — chiefly the unincorporated Leyden area west of Arvada (a historic 1902 coal-mine company town) and other foothills pockets. Jefferson County's own water-supply page frames the split plainly: water in the plains area is generally provided by water districts, while "if you live in the mountains, water is generally supplied via wells."

Those foothills wells draw from the Denver Basin bedrock aquifers (the Dawson Arkose, Denver, Arapahoe, and Laramie–Fox Hills) and, further west, fractured Precambrian crystalline rock. The signature concern is radon: Jefferson County Public Health notes that "in Colorado, radon in well water averages well above the proposed MCL," and the granitic sediments in the Dawson Arkose — the unit underlying the Arvada area — are a documented source of uranium and radon. In USGS sampling of Denver Basin drinking-water wells, radon and manganese were the only two constituents that exceeded human-health benchmarks in more than one well. Test a foothills well for radon first, then uranium, manganese, bacteria, and nitrate.

A Local Wrinkle: Uranium in the Source Watershed

Arvada's source watershed carries a specific uranium history. The Schwartzwalder uranium mine sits directly above Ralston Creek and Ralston Reservoir — roughly seven miles northwest of Golden, in the same watershed that supplies Arvada. After the operator went insolvent, the State of Colorado took over treatment in 2023; regulators have reported periodic untreated mine-water overflows to Ralston Creek historically, and the state-run treatment discharge is reported to meet water quality standards. The USGS-documented Leyden uranium prospect in the Laramie Formation coal west of Arvada is part of the same geology.

Rocky Flats, the former nuclear-weapons plant (1952–1992), is also northwest of Arvada near the North System corridor; CDPHE and DOE run ongoing environmental monitoring there, and no documented drinking-water violation from it was found for Arvada's supply. Both Denver Water and the City of Arvada monitor their source water and maintain source-water protection plans.

Municipal Water Quality

The City of Arvada's 2026 Water Quality Report (2025 data), covering surface water only with no wells, showed no violations. Lead at the 90th percentile was 3.1 ppb at customer taps (action level 15; no samples above the action level), copper 0.11 ppm (action level 1.3), disinfection byproducts well under limits, and naturally occurring fluoride around 0.5–0.7 ppm. UCMR5 screening found all 29 PFAS compounds non-detect. The water is soft (total hardness around 43–65 ppm). Arvada runs an active lead and pre-1960-galvanized service-line replacement program.

Denver Basin Depletion: Stable at the Western Margin

Because Arvada's municipal supply is entirely surface water, Denver Basin depletion does not affect the city's tap water — it matters only for the private wells and small systems on bedrock aquifers on the western fringe. There, the news is relatively good: Arvada sits at the basin's western recharge margin, where declines are minor. Colorado DWR monitoring shows a Denver-aquifer well in central Arvada (measured since 1961) holding steady at roughly 12–15 feet below land surface with no sustained decline, and a Jefferson County Arapahoe well stable over 2013–2022. That contrasts with the central and eastern basin, where USGS documents statistically significant declines of roughly 0.2 to 0.7 feet per year.

What Arvada Residents Should Know

If you're on City of Arvada water (almost everyone is): your water is treated mountain surface water meeting all standards, with clean PFAS results; the action item is whether you have an older lead or galvanized service line, which the city replaces.

If you're on a private well on the western foothills fringe (Leyden and nearby): test for radon first (the documented local priority), then uranium, manganese, bacteria, and nitrate. See our testing guide and radon page, and our Golden page for more on the same foothills geology.