Cal. Health and Safety Code § 6823

The district may contract with the Federal Government of the United States or any branch thereof, or with any county, city and county, municipal corporation, district or other public corporation or with any person, firm or corporation, for the joint acquisition or construction or use of any sewer or sewers or other works or facilities for the handling, treatment or disposal of sewage or industrial waste from the district and such other area as may be designated in said contract, when in the judgment of the legislative body of said district it is for the best interests of the district so to do. Any such contract may provide for the construction and maintenance of such sewer or sewers, or such other works or facilities, and for the payment by or for the parties thereto of such proportionate part of the cost of the acquisition, construction or maintenance of such sewer or sewers or other works or facilities as may be stated in said contract, the payments to be made at such times and in such amounts as may be provided by said contract. Any such contract may provide for the joint use of any sewer or sewers, works or facilities for the handling, treatment or disposal of sewage or industrial waste upon such terms and conditions as may be agreed upon by the parties thereto, and for the flowage, treatment or disposal of sewage or industrial waste from such area for each of the parties thereto as may be described in the contract. Any district which has acquired or constructed or which proposes to acquire or construct, any sewer or sewers, or works or other facilities for the handling, treatment or disposal of sewage or industrial waste, may contract with the Federal Government of the United States or any branch thereof, or with any county, city and county, municipal corporation, district or other public corporation or with any person, firm or corporation for the use of any such sewer or sewers, works or facilities by any such county, city and county, municipal corporation, district or other public corporation, or for the flowage, treatment or disposal of sewage or industrial waste from any area designated by such person, firm or corporation so contracting, upon such terms and conditions as may be provided in said contract.