Cal. Wat. Code § 43005
The board may enter into contracts with any or all interested parties for settlement or determination of any or all water rights on any stream system or on any part thereof which concerns the district or for the administration of water rights or of waters of any such stream system or any part thereof, whether by watermaster or otherwise; and if, in connection with any such contract and to make such contract efficiently operable for the benefit of the district, the board shall expressly find that the district should act for others also, whether their lands and water rights are within or without the district, then the district, with the written approval of any interested party for whom the district undertakes to act, may do so to the extent and under the terms which are expressed in any such contract.
Ca. Water Code § 43005