Coconino County, Arizona: drinking water report. Coconino County in northern Arizona is the second-largest county in the country by area, with about
Coconino County in northern Arizona is the second-largest county in the country by area, with about 145,000 residents including Flagstaff and portions of the Navajo Nation and Hopi Reservation. Water comes from deep groundwater wells tapping the Coconino Aquifer and the C-Aquifer (Redwall-Muav system). Water scarcity is a structural reality – Flagstaff has imposed water restrictions during drought years, and rural areas often haul water from distant fill stations.
Uranium mining is the defining water quality legacy in Coconino County. The Orphan Mine on the South Rim of the Grand Canyon and hundreds of abandoned uranium mines from the Cold War era left contaminated waste across the county. According to the EPA's 2024 Navajo Nation uranium contamination assessment, over 500 abandoned uranium mines exist across the Navajo portion of Coconino County, with documented contamination of springs and wells.
The USGS's 2024 groundwater study found uranium above the MCL of 30 ug/L in 8% of sampled wells on the Navajo Nation within Coconino County. Arsenic, a companion contaminant in uranium-bearing rock, was detected above 10 ppb in 12% of wells. These communities often lack alternative water sources.
Coconino County's water challenges are most acute on the Navajo Nation, where many residents rely on unregulated water sources that may be contaminated by uranium mining waste. If you haul water, verify that the fill station is tested and approved.
Check your water for any available data. For uranium and arsenic, reverse osmosis is the most effective household treatment. Our water filter guide covers systems certified for naturally occurring and mining-related radionuclides. Get your detailed report for local data, and visit our Arizona page for statewide context.