WAT § 35520.2

If a district determines to exercise the powers granted by this chapter, the district shall prepare and adopt a plan of works and an estimate of the amount of money necessary to be raised for the implementation of the plan of works. The estimate shall include contingencies, bond issuing expenses, provision for a reserve for bond discount not in excess of 10 percent of the total amount of the assessment, provision for a bond reserve not in excess of 15 percent of the total amount of the assessment, all expenses estimated to be incurred in complying with the procedures required by this chapter, cost of acquisition of land and rights of way, construction costs, provision for inflation, and all other costs properly chargeable to the plan.