Arizona Water Factsheets … Did You Know?
Pinal County Relies on Surface Water
Pinal County, Arizona's third most populous county, spans two diverse landscapes — in the east, the grasslands and woodlands of the Madrean Archipelago (Sky Islands), and in the west, the Sonoran Desert, with areas of agricultural and urban development punctuated by mountain peaks. Surface water has been the main source of water in Pinal County since the 1990s, when the Central Arizona Project (CAP) canal began delivering Colorado River water to central Arizona. In 2020, groundwater was the source of 45% of Pinal County’s water demand. Although most of the surface water used in Pinal County is delivered by the CAP, average annual precipitation, which ranges from 7–25 inches, supports perennial flows in the Lower San Pedro and Gila Rivers. The ephemeral Santa Cruz River also flows through the county.
In Arizona, surface water allocations are determined by the doctrine of prior appropriation, otherwise known as "first in time, first in right." However, the use of Colorado River water is managed by the Arizona Department of Water Resources and the US Bureau of Reclamation, which in 2021 began mandating Tier 1 shortage reductions in water deliveries following years of declining water levels in Lake Mead. The brunt of CAP reductions is borne by agriculture, which, until the reductions were introduced, accounted for 90% of CAP water demand within the Pinal Active Management Area (AMA). As a result of CAP reductions, groundwater pumping has increased, making the Pinal AMA’s “safe-yield” groundwater conservation goal more difficult to achieve. A potential consequence of increased groundwater use is overdraft (pumping more water from an aquifer than is recharged), which can cause damaging land subsidence, a sinking ground level, and earth fissuring. Water resource managers are working to manage water portfolios to mitigate uncertainties in water supplies resulting from local drought and Colorado River shortage conditions.