California Code, Water Code - WAT § 2502

If the board finds that the use by any persons under claim of right of only minor quantities of water, as defined in Section 2503, would have no material effect on the rights of other claimants, the board may exempt such persons from being subject to these proceedings as claimants or parties with respect to such minor quantities of water;  provided, that any person so exempted may elect to continue to be subject to these proceedings by giving prompt notice to the board.