For the purposes of ORS § 225.320, the city governing body may, after referring the question of acquiring and constructing the facilities to a vote of the electors of the city and after approval thereof by a majority of the electors, authorize the issuance of and cause to be issued bonds of the city for such purposes, either general obligation, limited obligation or self-liquidating in character, in a sum not more than the amount authorized at such election and subject to the provisions of ORS § 225.370 and 225.380. Bonds so authorized and issued may provide for payment of both principal and interest thereon from service charges to be imposed by the city governing body for services to be extended and through employment and use of the irrigation and fire protection facilities. If service charges are imposed to be so paid, such portion thereof as may be deemed sufficient shall be set aside as a sinking fund for payment of interest on the bonds and the principal thereof at maturity.