Well Water in Denver, Colorado

Denver County · Population ~715,000 · Aquifer: Municipal mountain surface water; Denver Basin wells are a rare fringe case

Hardness: Soft to moderately hard (municipal); harder in Denver Basin groundwater

Denver's Water Comes From the Mountains, Not Underground

Denver Water's supply is treated surface water, split roughly evenly between the Colorado River system on the West Slope and the South Platte system on the East Slope. West Slope water crosses the Continental Divide through the roughly 23-mile Harold D. Roberts Tunnel (from Dillon Reservoir, the utility's largest) and the Moffat Collection System, which gathers dozens of Grand County streams into Gross Reservoir. The water is then treated at Front Range plants including Marston, Foothills, and the newer Northwater facility.

Denver has been on piped surface water since the 19th century and municipalized its system in 1918. An 1880s artesian-well boom once put on the order of 150 wells within the city, but the mature municipal system displaced them long ago.

Private Wells: A Rare Fringe Case

Within Denver city limits, private wells are uncommon. Where they exist — on the rural, industrial, and unincorporated edges, and in the suburbs outside the city — they draw from the Denver Basin bedrock aquifer system: the stacked Dawson, Denver, Arapahoe, and Laramie–Fox Hills formations, plus shallow alluvial aquifers along the South Platte and Cherry Creek valleys. The Denver Basin aquifers are designated and regulated by the Colorado Division of Water Resources, and new exempt wells face permitting limits because the deep bedrock water is essentially nonrenewable.

The much bigger Denver Basin well story belongs to the suburbs to the south and east — Douglas County, Parker, Highlands Ranch — not the City of Denver itself.

What's in Denver Basin Groundwater (For the Few Wells)

For the rare Denver-area well, the relevant science is the USGS study of Denver Basin groundwater quality (SIR 2014-5051, Musgrove et al. 2014, and the earlier Circular 1357). Radon was the standout: concentrations exceeded the lower proposed EPA drinking-water standard in more than 90 percent of the bedrock-aquifer samples where it was measured (but exceeded the higher alternative standard in less than 5 percent). Radon was most pronounced in the Dawson aquifer, associated with uranium-bearing granitic sediments. Only manganese and radon exceeded a human-health benchmark in more than one sample across the basin.

Radium, uranium, and manganese are naturally occurring in the basin's bedrock groundwater. Colorado is also an EPA Radon Zone 1 state (highest potential). If you are on a private well in the Denver area, test for radon, radium, uranium, manganese, bacteria, and nitrates.

The Municipal Water: Quality and the Lead-Pipe Story

Denver Water reports that its treated supply meets or exceeds all federal and state drinking-water standards, collecting on the order of 63,000 samples and 145,000 tests in a recent reporting year. Denver Water classifies its water as "soft to moderately hard," varying by distribution zone and season — much softer than the Denver Basin groundwater under the city.

The notable local water-quality issue is not the source water but the pipes: Denver Water has identified on the order of 65,000 lead service lines in its system and is roughly halfway through a multi-hundred-million-dollar Lead Reduction Program, replacing lead and galvanized lines with copper at no direct charge to the homeowner. In 2018 the state required the utility to add orthophosphate for corrosion control as an interim measure. If you live in an older Denver home, the lead risk is your service line and plumbing, not the water leaving the treatment plant.

What Denver Residents Should Know

If you're on Denver Water (almost everyone is): your water meets all standards; the thing to act on is whether you have a lead service line, which the utility will replace free. Review Denver Water's annual Water Quality Report for the latest detections.

If you're on a private well (rare, mostly the fringe): test for radon, radium, uranium, manganese, bacteria, and nitrates. Radon in the Denver Basin bedrock is common and worth checking. See our testing guide for labs and costs, and our radon page for treatment options.