Cochise County, Arizona: drinking water report. Cochise County spans southeastern Arizona from the Chiricahua Mountains to the San Pedro River Valley, with…
Cochise County spans southeastern Arizona from the Chiricahua Mountains to the San Pedro River Valley, with major communities including Sierra Vista, Bisbee, Willcox, and Douglas. The county relies almost entirely on groundwater from the Upper San Pedro and Willcox basins, with minimal surface water sources in this arid region. Water supply in Cochise County faces pressure from decades of mining activity, agricultural irrigation, and growing residential demand near Fort Huachuca.
Groundwater throughout Cochise County shows contamination patterns tied to both natural geology and human activity. Arsenic appears in many wells across the county at levels above EPA standards, leaching naturally from volcanic rock formations that define much of the region's geology. The Willcox basin in particular shows elevated arsenic concentrations that reflect the area's mineral-rich bedrock rather than pollution.
Historic copper mining around Bisbee and other mountain communities left a different signature. Old mine tailings and processing sites released metals including lead, cadmium, and copper into surrounding soils and groundwater. While major remediation efforts have addressed the worst contamination, metals persist in some residential wells near former mining operations. The Sierra Vista area draws from aquifers that show generally better quality but face declining water tables from sustained pumping.
Nitrate contamination affects agricultural areas, especially around Willcox and the Sulphur Springs Valley where decades of fertilizer application have pushed levels above the 10 mg/L drinking water standard in scattered wells. Small water systems serving rural subdivisions sometimes lack the treatment capacity to address these multiple contaminants effectively. PFAS testing remains limited in the county, though military activity at Fort Huachuca and associated fire training raises questions about potential contamination in nearby groundwater.
Residents using private wells should test annually for arsenic, nitrate, and metals given the county's geology and land use history. Those near former mining areas or agricultural zones face higher risk and may benefit from point-of-use treatment systems. Check your water to see current data for your area, review our water filter guide for treatment options suited to Arizona's specific contaminants, access your detailed report for comprehensive testing recommendations, or visit the Arizona state page for broader context on water quality across the region.
Drinking water is one exposure route. These federal datasets also cover Cochise County, AZ.
The EPA places Cochise County, AZ in Zone 2 - a moderate-risk category, with a predicted average indoor radon level between 2 and 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.
40% of homes in Cochise County, AZ 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 Cochise County, AZ averages 5.9 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 34 public water systems serving Cochise County, AZ with EPA lead testing on record, 2 (5.9%) reported a 90th-percentile lead result above the EPA's 15 ppb action level, and the median is 2.3 ppb. 22 water systems serving Cochise County, AZ carry a health-based EPA Safe Drinking Water Act violation.
| Most-cited violation type | Systems affected |
|---|---|
| Lead and Copper Rule Revisions | 16 |
| Revised Total Coliform Rule | 8 |
| Ground Water Rule | 6 |
| Arsenic | 2 |
| Fluoride | 2 |
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.