Jefferson County, Colorado: drinking water report. Jefferson County borders Denver to the west and stretches into the foothills, serving about 580,000…
Jefferson County borders Denver to the west and stretches into the foothills, serving about 580,000 residents. Water here comes from a complex web of providers – Consolidated Mutual Water Company, the City of Arvada, the City of Lakewood, and several metro districts each operate independently. Sources include a mix of mountain reservoir water, South Platte River diversions, and Denver Water wholesale purchases. That fragmentation means two houses on the same street can receive water from entirely different systems with different source blends.
The former Rocky Mountain Arsenal, a chemical weapons manufacturing facility just northeast of Jefferson County in neighboring Adams County, created a contamination legacy that affects regional groundwater. While the Arsenal itself is now a National Wildlife Refuge, dissolved-phase contaminants have migrated through the Denver Basin aquifer system. The Rocky Flats Plant – a former nuclear weapons production facility in the northern part of Jefferson County – adds plutonium and chemical contamination to the area's environmental history.
According to the Colorado Department of Public Health and Environment's 2024 monitoring data, three public water systems in Jefferson County reported PFAS detections during UCMR5 sampling. Buckley Space Force Base in adjacent Arapahoe County is a confirmed PFAS source that shares the same regional aquifer system.
Identifying your actual water provider is step one in Jefferson County – the answer is not always obvious, and it determines your source water and contaminant profile entirely.
Check your water to see data specific to your provider and ZIP code. For PFAS or legacy industrial contaminants, reverse osmosis provides the broadest household protection. Our water filter guide ranks systems by certified performance. For historical trends, pull your detailed report. Visit our Colorado page for the statewide picture.
Drinking water is one exposure route. These federal datasets also cover Jefferson County, CO.
The EPA places Jefferson 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.
52% of homes in Jefferson County, CO were built before 1980, and 5% 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 Jefferson County, CO averages 5.8 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
Across 89 public water systems serving Jefferson County, CO with EPA lead testing on record, 1 (1.1%) reported a 90th-percentile lead result above the EPA's 15 ppb action level, and the median is 3 ppb. 25 water systems serving Jefferson County, CO carry a health-based EPA Safe Drinking Water Act violation.
| Most-cited violation type | Systems affected |
|---|---|
| Stage 1 Disinfectants and Disinfection Byproducts Rule | 8 |
| Lead and Copper Rule | 6 |
| Surface Water Treatment Rule | 5 |
| Ground Water Rule | 4 |
| Interim Enhanced Surface Water Treatment Rule | 4 |
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.