Prior to supplying any water, the board of county commissioners must determine and find the following: the amount necessary in each year to pay the principal of and the interest on the water revenue bonds proposed to be issued to finance such system; the amount necessary to be paid each year into any reserve funds which the board of county commissioners may deem it advisable to establish in connection with the retirement of the proposed water revenue bonds and the maintenance of the system. The determinations and findings of the board of county commissioners required to be made in the preceding sentence shall be set forth in the proceedings under which the proposed water revenue bonds are to be issued and such findings shall be the basis for determining the cost of the water to the inhabitant consumers.