All powers granted to reservoir improvement districts incorporated under the provisions of this act shall be exercised by a board of directors which shall be composed of an odd number of directors not less than three nor more than five as specified in the petition for creation of the district. Each director shall serve for a term of three years, and until a successor is elected and qualified, except that as nearly as possible 1/3 of the original board members designated in the petition for organization of the district shall serve for a term of one year, 1/3 for a term of two years and 1/3 for a term of three years. Such directors shall serve without compensation, but shall be allowed actual and necessary expenses incurred in the performance of their official duties.