Cal. Health and Safety Code § 4793.1

When the purposes and objects mentioned in the resolution calling the bond election have been accomplished, any moneys remaining in the construction fund may be transferred to the fund to be used for the payment of principal and interest on the bonds. The district board by a vote of two-thirds of the members thereof may use said remaining moneys for some other county sanitation district purpose which will benefit the property in the district or improvement district, as the case may be; provided, however, that with respect to improvement districts such general objectives and purposes shall not include the acquisition or construction of new local street sewers or laterals as distinguished from main trunks, interceptors, and outfall sewers. Said moneys may not be used for said other county sanitation district purposes until two-thirds of the qualified electors of said district or improvement district thereof, as the case may be, have consented thereto at a special election called in said district or improvement district by the district board. Notice of said election shall be given and said election shall be held and conducted in the manner provided for bond elections in said county sanitation district or improvement district, as the case may be.