(1) In any county the county legislative authority may by resolution establish a county purchasing department.
(2) In each county with a population of less than four hundred thousand which exercises this option, the purchasing department shall contract on a competitive basis for all public works, enter into leases of personal property on a competitive basis, and purchase all supplies, materials, and equipment, on a competitive basis, for all departments of the county, as provided in this chapter and chapter 39.04 RCW, except that the county purchasing department is not required to make purchases for the county hospital, or make purchases that are paid from the county road fund or equipment rental and revolving fund.