The roll approved and certified to the county officers by the board of county commissioners as in this chapter provided shall constitute the valuations of land, buildings and improvements furnished protection and services by the systems of the district against which valuation taxes shall be levied and collected annually in the same manner as general taxes for the continuing operations of the district and its systems. The valuations on said roll shall be subject to adjustment from time to time in the manner provided in RCW
85.15.060.