Cal. Water Code § 13897.3

The department shall annually establish the interest rate for loans made pursuant to this chapter at 50 percent of the average interest rate, computed by the true interest cost method, paid by the state on general obligation bonds for the prior calendar year. 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.