Cal. Gov. Code § 53393

The legislative body may pledge any source of revenues, in addition to any property tax revenues, to pay the principal and interest on bonds approved and issued pursuant to this chapter, including, but not limited to, any fees or charges for services provided by, or in conjunction with, facilities rehabilitated with the proceeds of any bond issuance as long as those fees or charges do not exceed the estimated reasonable cost of providing the service for which the fee or charge is imposed.