Cal. Water Code § 51522

All money, including interest and penalties, derived by sale or otherwise, from original and additional assessments shall be placed by the county treasurer of the principal county to the credit of the general fund of the district or, if bonds of the district have been issued upon the assessment and remain unpaid and provision has not been made for the payment thereof, shall be deposited in a separate fund for the sole purpose of paying the principal and interest of the bonds and the expenses of the county treasurer.