amount equal to the rate of inflation as compared to existing rates. The interim rates shall be effective on the first day of the first test year in the general rate case application. These interim rates shall be subject to refund and shall be adjusted upward or downward back to the interim rate effective date, consistent with the final rates adopted by the commission. The commission may authorize a lesser increase in interim rates if the commission finds the rates to be in the public interest. If the presiding officer in the case determines that the commission’s decision cannot become effective on the first day of the first test year due to actions by the water corporation, the presiding officer or commission may require a different effective date for the interim rates or final rates.

pursuant to the plan every three years. The plan shall include a provision to allow the filing requirement to be waived upon mutual agreement of the commission and the water corporation.