California Code, Water Code - WAT § 71972

Any moneys remaining in the special improvement fund from the sale of bonds of the district after the purpose for which the indebtedness was created has been accomplished may also be used for any other municipal water district purpose.  Such moneys remaining from the sale of bonds of the district for an improvement district therein may also be used for any purpose which will benefit the property in the improvement district.

Such moneys may not be used for such other municipal water district purpose or improvement district purpose until two-thirds of the qualified voters of the district or improvement district have consented thereto at a special election called in the district or improvement district by the board.  Notice of the election shall be given in the manner provided for bond elections in the district or improvement district, as the case may be, and in other respects the election shall be conducted as are other district elections.