The Contra Costa Water District may provide for bonds of the district to bear a variable interest rate, which rate shall not at any time exceed the maximum rate permitted by Section 53531 of the Government Code or any other applicable provision. If the rate of interest is variable, the resolution adopted pursuant to Section 31391 shall state the manner and intervals at which the rate shall vary, and all bonds shall recite on their face the manner and the intervals at which the rate may vary.