In performing their duties under the provisions of this title the board and members of the board of drainage commissioners 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 such services and compensation are allowed and approved at a regular meeting of the board. Upon the submission of a copy, certified by the secretary, of the extracts of the relevant minutes of the board showing such approval, to the county auditor, the same shall be paid as other claims against the district are paid. 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.

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.