What factor suggests that Phoenix does not have to worry about its water supply?

The indication that Phoenix does not have to worry about its water supply relates to its water rights associated with agricultural activities. Water rights are legal entitlements allowing holders to use a certain amount of water from a finite source. In arid regions like Phoenix, which is located in the Sonoran Desert, agriculture has historically been a significant user of water resources. The established water rights benefit the city by ensuring a reliable source of water for both agricultural and municipal needs. This system allows for the allocation and management of water resources, which is crucial in a desert environment where water scarcity is a common concern.

The other factors presented do not provide the same level of assurance regarding the availability of water in Phoenix. Climate change introduces uncertainty regarding water supplies, and changing rainfall patterns can lead to variations in available water. Relying on desalination as a solution for future water shortages may have potential, but it involves significant economic and environmental considerations that affect feasibility. Therefore, the established water rights tied to agricultural activities are a robust factor in ensuring a stable water supply for Phoenix.