Well Water in Prescott / Prescott Valley / Chino Valley, Arizona

Yavapai County · Population ~120,000 (Prescott AMA) · Aquifer: Prescott AMA Basin-Fill Alluvial Aquifers

Hardness: Moderate to Hard

Arsenic in the Prescott AMA

ADEQ's ambient groundwater quality study of the Prescott AMA found that 6 of 58 sampled sites exceeded EPA Primary Maximum Contaminant Levels, with arsenic exceedances at four sites, fluoride at three sites, and barium, gross alpha, and nitrate at one site each.

But the problem is worse than the AMA-wide numbers suggest. Specific areas are severely affected:

• Paulden and southern Chino Valley — very high arsenic levels in groundwater
• Dewey-Humboldt area — wells exceed the arsenic MCL, compounded by soil contamination near the Iron King Superfund site
• Cornville — in 2004, six well water samples ranged from 15 to 952 micrograms per liter of arsenic. The EPA limit is 10.

The City of Prescott manages arsenic in its public supply by blending water from wells with different concentrations. Private well owners have no such option — you get whatever your well produces.

The Overdraft Problem

The Prescott AMA has been designated an Active Management Area since the 1980 Groundwater Management Act — one of Arizona's original five AMAs. Despite decades of management, the basin remains in chronic overdraft.

As of 2019, almost three-quarters of the AMA's total demand was supplied by groundwater overdraft. The primary water source in Yavapai County is groundwater at 78%, with surface water at 21% and reclaimed water at just 1%.

For well owners, chronic overdraft means declining water tables, increasing pumping costs, and potentially worsening water quality as deeper, more mineralized water is drawn into the system.

Fluoride and Other Contaminants

Fluoride is the second most common health-based water quality exceedance in the Prescott AMA after arsenic. Both appear to be naturally occurring — they tend to occur at sites with water chemistry different from the prevalent calcium-bicarbonate type found across most of the basin.

ADEQ's study found that regional groundwater quality generally supports drinking-water uses, but the exceptions are significant. The naturally occurring contaminants cluster in specific geological zones, making location everything.

Nitrate was generally below natural background levels across the AMA, except near the Dewey-Humboldt area where older septic systems and agricultural activity have contributed elevated levels.

What Prescott Area Well Owners Should Do

Test your water for arsenic — this is not optional in Yavapai County. AZDHS recommends testing every five years at minimum, but given the variability in this area, every two to three years is more prudent.

Also test for fluoride, nitrate, bacteria, and a basic mineral panel. If you're near Dewey-Humboldt or any historical mining area, add a heavy metals panel.

If arsenic exceeds 10 ppb, a point-of-use reverse osmosis system at the kitchen sink is the most cost-effective immediate step — typically $300-$600 installed. It won't treat your shower water, but it protects your drinking and cooking water. See our testing guide for labs and costs.