Cal. Water Code § 1745.04

A water supplier may contract with a state drought water bank or with any other state or local water supplier or user inside or outside the service area of the water supplier to transfer, or store as part of a transfer, water if the water supplier has allocated to the water users within its service area the water available for the water year, and no other user will receive less than the amount provided by that allocation or be otherwise unreasonably adversely affected without that user’s consent.