Each calendar year, the governing body shall establish the rate of the service surcharge, not to exceed the amount authorized by section 86-435, that together with any surplus revenue carried forward will produce sufficient revenue to fund the expenditures described in section 86-421. Amounts collected in excess of such necessary expenditures within a given year shall be carried forward to the next year. A governing body shall make its determination of the rate no later than September 1 of each year and, if it is a new rate, shall fix the new rate to take effect commencing with the first billing period of each service user on or following the next January 1. The governing body shall notify by certified or registered mail every service supplier of any change in the rate at least ninety days before the new rate becomes effective.