Cal. PCC § 21051

All contracts for the construction or extension of any waterworks, water system or water distribution system, or for furnishing labor, materials or supplies therefor as herein provided, shall be let to the lowest responsible bidder. The legislative body of such city shall advertise for two or more days in a newspaper of general circulation printed and published in such city, inviting sealed proposals for furnishing labor, materials and supplies for the proposed waterworks, water system or water distribution system before any contract shall be made therefor. The said legislative body shall have the right to require such bonds as it may deem best from the successful bidder to insure the faithful performance of the contract, and shall also have the right to reject any and all bids; provided, however, that nothing herein contained shall be construed as prohibiting the municipality itself from constructing or extending such waterworks, water system, or water distribution system and employing the labor necessary therefor, without a contractor; and provided further, that in municipalities operating under a charter heretofore or hereafter framed under the provisions of the Constitution of the State of California, all acts required to be performed subsequent to the sale of such bonds by this act, shall be done and performed by the proper body, board, officer, or commission of such municipality, as is required or authorized by such charter to perform such acts, and in case such charter also prescribes the manner of letting and entering into contracts for the furnishing of labor, materials, or supplies for the constructing or extending of such waterworks, water system, or water distribution system, the contracts therefor shall be let and entered into in conformity with such charter.