The members of the board may receive as compensation up to ninety dollars per day or portion thereof spent in actual attendance at official meetings of the district, or in performance of other official services or duties on behalf of the district: PROVIDED, That such compensation shall not exceed eight thousand six hundred forty dollars in one calendar year: PROVIDED FURTHER, That the board may fix a different salary for the secretary thereof in lieu of the per diem. Each commissioner is entitled to reimbursement for reasonable expenses actually incurred in connection with such business, including subsistence and lodging, while away from the commissioner's place of residence, and mileage for use of a privately owned vehicle in accordance with chapter 42.24 RCW. The salary and expenses shall be paid by the treasurer of the fund, upon orders made by the board. Each member of the board must before being paid for expenses, take vouchers therefore from the person or persons to whom the particular amount was paid, and must also make affidavit that the amounts were necessarily incurred and expended in the performance of his or her duties.

Any commissioner may waive all or any portion of his or her compensation payable under this section as to any month or months during his or her term of office, by a written waiver filed with the secretary as provided in this section. The waiver, to be effective, must be filed any time after the commissioner's election and prior to the date on which the compensation would otherwise be paid. The waiver shall specify the month or period of months for which it is made.

The dollar thresholds established in this section must be adjusted for inflation by the office of financial management every five years, beginning January 1, 2024, based upon changes in the consumer price index during that time period. "Consumer price index" means, for any calendar year, that year's annual average consumer price index, for Washington state, for wage earners and clerical workers, all items, compiled by the bureau of labor and statistics, United States department of labor. If the bureau of labor and statistics develops more than one consumer price index for areas within the state, the index covering the greatest number of people, covering areas exclusively within the boundaries of the state, and including all items shall be used for the adjustments for inflation in this section. The office of financial management must calculate the new dollar threshold and transmit it to the office of the code reviser for publication in the Washington State Register at least one month before the new dollar threshold is to take effect.

A person holding office as commissioner for two or more special purpose districts shall receive only that per diem compensation authorized for one of his or her commissioner positions as compensation for attending an official meeting or conducting official services or duties while representing more than one of his or her districts. However, such commissioner may receive additional per diem compensation if approved by resolution of all boards of the affected commissions.