Cal. Water Code § 55662

If the board determines that the proposed improvement will not be of district-wide benefit, the board may make such changes in the boundaries of the proposed zone as may be deemed advisable and shall define and establish the boundaries, but shall not modify the boundaries so as to exclude from the proposed zone any territory which will be benefited by the improvement, nor to include in the proposed zone any territory which, in its judgment, will not be benefited by the proposed improvement.