For the purpose of paying the cost of any such water service extension or sanitary sewer service extension, in any such district, the city council or board of trustees may, by ordinance, cause bonds of the municipality to be issued, called district water service extension bonds of district No. .... or district sanitary sewer service extension bonds of district No. ...., payable in not exceeding twenty years from date and to bear interest payable annually or semiannually with interest coupons attached. The ordinance effectuating the issuance of such bonds shall provide that the special tax and assessments shall constitute a sinking fund for the payment of such bonds and interest. If a written protest, signed by owners of the property located in the improvement district and representing a majority of the front footage which may become subject to assessment for the cost of the improvement, is filed with the municipal clerk within three days before the date of the meeting for the consideration of such ordinance, such ordinance shall not be passed. The entire cost of such water extension mains or sanitary sewer extension mains in any such street, avenue, or alley may be chargeable to the private property therein and may be paid by the owner of such property within fifty days from the levy of such special taxes and assessments, and thereupon such property shall be exempt from any lien for the special taxes and assessments. The bonds shall not be sold for less than their par value. If the assessment or any part thereof fails or for any reason is invalid, the governing body of the municipality may, without further notice, make such other and further assessments on the lots and lands as may be required to collect from the lots and lands the cost of the improvement, properly chargeable as provided in this section. In lieu of such general obligation bonds, the municipality may issue revenue bonds as provided in section 18-502, to pay all or part of the cost of the construction of such improvement.