California Code, Public Contract Code - PCC § 20611

Under no circumstances shall the total amount of all reimbursement payments made or agreed to be made exceed the amount, specified in said contract, for the total cost of the water system facilities exclusive of the costs attributable to the land of the installer. An amount attributable to interest may also be included in the contract, at a rate not to exceed 4 percent per annum from the date of installation to the date of connection of other land to the facilities.