Is Tucson's 47 years' worth of groundwater enough if CAP is slashed?

Tucson Water could lose between 6% and nearly 85% of its Colorado River water, depending on how deeply the Central Arizona Project is cut. The U.S. Bureau of Reclamation is expected to identify its preferred plan soon, with new reductions potentially starting next year.

Tucson currently has the legal right to receive nearly 45% more CAP water than customers use. Since the early 2000s, the utility has stored much of that extra water underground for future needs. Even if the federal government eliminated the CAP’s supply, Tucson would have at least 10 years of stored project water, according to the report.

Altogether, Tucson’s stored CAP water and other groundwater reserves total about 4.7 million acre feet, equal to roughly 47 years of supply at the city’s current use. However, those reserves are limited. If CAP deliveries fall below customer demand, the city could eventually need to increase conservation, use more groundwater or pay for new supplies from stormwater capture, wastewater treatment or other projects.

Tucson Water officials say the community can avoid a crisis through conservation and long term planning. Per person water use has fallen by about one third since 2000, to less than 80 gallons a day. Some city leaders and University of Arizona researchers, however, want faster action on conservation, stormwater projects and policies requiring new development to offset its water use.