California Code, Water Code - WAT § 60230.5

All expenditures for construction work, materials, equipment and supplies, and professional services, including, but not limited to, legal, legislative, public affairs, public relations, and engineering services, regardless of price shall be made pursuant to contract.  All district contracts shall be in writing in a form prescribed by the general manager and approved by the general counsel.  At minimum, each contract shall include the relevant scope of work, duration, and terms of payment.