Cal. Health and Safety Code § 4730.7

The governing board of the Delta Diablo Sanitation District may designate any depository or depositories pursuant to Article 2 (commencing with Section 53630) of Chapter 4 of Part 1 of Division 2 of Title 5 of the Government Code for the custody of any or all revenue collected or received for operation and maintenance purposes. All moneys deposited with a designated depository or depositories shall be invested in checking accounts, savings accounts, certificates of deposit, or other insured accounts. All other district revenue, including any moneys collected or received for the payment of principal and interest on district bonds, other indebtedness, or certificates of participation, and any moneys designated for capital outlay expenditure shall be paid into the county treasury to the credit of the district. Every designated depository shall give security sufficient to secure the district against possible loss and shall pay the warrants or checks drawn by the district for demands against the district under any rules as the governing board may prescribe.