Tempe Water Hardness & Quality Report (2026)

Tempe, Arizona draws its municipal water supply from the City of Tempe Water Resources Division, sourcing from the same regional blend that serves greater Phoenix: surface water from Salt River Project canals connected to Roosevelt, Apache, Canyon, and Saguaro Reservoirs on the Salt River and Verde River systems; imported Colorado River water via the Central Arizona Project (CAP) Aqueduct from Lake Havasu; and local groundwater pumped from the Phoenix Active Management Area alluvial aquifer in Maricopa County. Water is treated at Tempe's water treatment facilities in compliance with Arizona DEQ standards. Water hardness in Tempe reaches 420 mg/L — extremely hard and among the highest for any major Arizona city.

Tempe's extreme hardness is a consequence of the same geological and climatic factors that drive very high hardness throughout the Phoenix Basin. Colorado River water travels through extensive Permian Kaibab Limestone, Triassic Moenkopi Formation, and Jurassic carbonate canyons before reaching Lake Havasu, arriving heavily mineralised. Salt River impoundments collect calcium-rich runoff from the Sonoran Desert's Mazatzal Mountains metamorphics and desert carbonate soils. Groundwater from the Phoenix Basin alluvial aquifer — composed of deep Quaternary and Tertiary alluvial fans and ancient lake deposits — is further concentrated by the region's extremely high evapotranspiration rates, producing the very high dissolved mineral content characteristic of all greater Phoenix water supplies.

At 420 mg/L, Tempe residents — including the large Arizona State University student population — face extreme scale challenges. Showerheads and faucet aerators clog rapidly with calcium deposits, and bathroom surfaces require frequent cleaning with descaling products. Water heaters experience accelerated element failure without regular professional servicing. Installing a whole-house water softener is standard practice for Tempe homeowners and long-term renters, and most plumbers consider it essential for protecting the city's plumbing infrastructure from premature scale-induced failure. Despite the hardness, Tempe Water Resources consistently delivers EPA-compliant, safe drinking water.