Cal. Water Code § 14024

The department shall establish the interest rate for loans made pursuant to this chapter at 50 percent of the true interest cost to the state of general obligation bonds issued most recently prior to the loan being executed. All loans made pursuant to this chapter shall carry the established interest rate for the calendar year in which the funds are committed to the loan, as of the date of the letter of commitment from the department, and shall remain at that interest rate for the duration of the loan.