Well Water in Green Valley / Sahuarita, Arizona
Pima County · Population ~40,000 · Aquifer: Upper Santa Cruz Basin
Hardness: Very Hard (15+ grains per gallon)
Green Valley sits in the mineral-rich Sonoran Desert of southern Arizona, drawing water from deep groundwater wells. The Community Water Company of Green Valley reports seven contaminants exceeding health advocacy guidelines, including arsenic, chromium (hexavalent), and radium. Water hardness measures an alarming 15 grains per gallon — among the most mineral-laden supplies in Arizona. The area's geological composition, shaped by volcanic activity and copper mineralization, contributes these contaminants naturally.
Arsenic and Radium from Desert Geology
Southern Arizona's Sonoran Desert geology contributes arsenic to groundwater throughout the region, and Green Valley is no exception. The deep groundwater wells that serve the community contact mineral-rich volcanic and sedimentary formations.
Key contaminants include:
- Arsenic — naturally occurring from the desert's geological composition. A known human carcinogen.
- Radium — radioactive elements that occur naturally in deep groundwater. Long-term exposure increases cancer and kidney damage risk.
- Chromium (hexavalent) — may be from regional mining/industrial activity or natural mineral deposits
The community water system treats and blends to meet legal limits. Private well owners get the raw groundwater.
Extreme Hardness
Green Valley's water measures approximately 15 grains per gallon (GPG) of hardness — classified as "very hard" and ranking among Arizona's most mineral-laden water supplies.
This extreme hardness is a direct result of the geology. Deep groundwater has been in contact with limestone, volcanic rock, and mineral deposits for thousands of years, dissolving calcium and magnesium along the way.
At 15 GPG, you'll see heavy scale buildup in water heaters (reducing efficiency and lifespan), white deposits on fixtures, and reduced effectiveness of soaps and detergents. A water softener is nearly essential for protecting plumbing and appliances.
Mining Legacy in the Santa Cruz Basin
Southern Pima County has a long history of copper mining — the area's economic backbone for over a century. Active and historical mining operations can contribute heavy metals to groundwater through acid mine drainage, tailings seepage, and disturbed geology.
The Rosemont Mine proposal (now the Copper World project) near Green Valley has raised water quality concerns for the Santa Cruz watershed. Whether or not new mining proceeds, the legacy of existing operations is already in the aquifer.
If you're on a private well near any mining operation — active or historical — a comprehensive metals panel should be part of your testing.
Testing Recommendations
Green Valley well owners should test for:
- Arsenic — essential given the geology
- Radium and gross alpha — natural radioactivity in deep wells
- Chromium — both total and hexavalent
- Nitrate — from septic systems and agricultural activity
- Hardness, TDS, fluoride — mineral baseline
- Heavy metals panel — if near mining operations
The Green Valley Domestic Water Improvement District publishes annual water quality reports at gvwaterdistrict.com. See our testing guide for private testing labs.
Every well is different. Two wells on the same street can produce completely different water. The data on this page reflects documented conditions in the Green Valley / Sahuarita area, but the only way to know what's in your water is to test it.
Sources
- Community Water Company of Green Valley — Water Quality Reports
- Green Valley Domestic Water Improvement District — Annual Reports
- ADEQ — Upper Santa Cruz Basin Groundwater Quality
- Arizona Geological Survey — Mineral Resources of Pima County