Mesa County, Colorado: drinking water report. Mesa County on Colorado's Western Slope has about 155,000 residents, with Grand Junction as the county seat.
Mesa County on Colorado's Western Slope has about 155,000 residents, with Grand Junction as the county seat. Water comes from the Colorado River and local reservoirs, managed by Ute Water Conservancy District and the City of Grand Junction. The county sits in a former uranium mining and milling region, and the Colorado River at Grand Junction carries dissolved salts and naturally occurring minerals from across its upper basin.
Uranium mill tailings from the Cold War era were piled along the Colorado River in Grand Junction for decades before a massive DOE cleanup moved over 4.3 million tons of material to a disposal cell in the 1990s. According to DOE's 2024 long-term surveillance report, residual contamination in groundwater near the former mill sites includes uranium, vanadium, and selenium at concentrations above background levels.
The Colorado River at Grand Junction is naturally high in TDS – averaging 500 mg/L – from dissolution of the Mancos Shale and other geological formations in the upper basin. A 2024 USGS study found selenium at 4 ppb in the river at Grand Junction – below the MCL of 50 ppb but part of the river's natural mineral load.
Mesa County's Colorado River supply carries the mineral signature of the upper basin, and the uranium milling legacy adds a contamination dimension that other Western Slope communities do not face. Treatment plants manage these inputs, but the source water starts with a higher mineral baseline.
Check your water for current data. For the high-TDS water typical of the Western Slope and any residual uranium-related concerns, reverse osmosis provides effective household treatment. Our water filter guide covers systems suited to Colorado River basin water. Pull your detailed report for trends, and visit our Colorado page for statewide context.
Drinking water is one exposure route. These federal datasets also cover Mesa County, CO.
The EPA places Mesa County, CO in Zone 1 - the EPA's highest-risk category, where the predicted average indoor radon level is above 4 pCi/L. Zone maps predict an area's radon potential from geology and existing indoor readings; they say nothing about a specific house. Testing is the only way to know your own level.
41% of homes in Mesa County, CO were built before 1980, and 10% before 1950. Residential lead paint was banned in 1978, so housing age is the strongest available proxy for lead-paint exposure. This describes the county's housing stock, not any one home.
Modelled annual fine-particle pollution (PM2.5) in Mesa County, CO averages 5.1 µg/m³, within the EPA's annual standard of 9 µg/m³. These are CDC modelled county estimates rather than readings from a specific monitor.
How radon zones work · Air quality by county · Lead exposure guide
9 public water systems serving Mesa County, CO have EPA lead testing on record. The reported lead sample skews toward systems that already flagged a problem, so its exceedance rate is not directly comparable with other areas. 1 water systems serving Mesa County, CO carry a health-based EPA Safe Drinking Water Act violation.
| Most-cited violation type | Systems affected |
|---|---|
| Interim Enhanced Surface Water Treatment Rule | 1 |
Source: EPA Lead and Copper Rule 90th-percentile tap sampling and EPA SDWIS Safe Drinking Water Act enforcement records, aggregated from the public water systems serving this county. Figures are counts of water systems, not a test of any individual home or tap.