To pay the original cost of water, light, power, or heat systems, every city of the second class may issue:

(1) General bonds to be retired by general tax levies against all the property within the city limits then existing or as they may thereafter be extended; or

(2) Utility bonds under the general authority given to all cities for the acquisition or construction of public utilities.

Extensions to plants may be made either

(1) By general bond issue,

(2) By general tax levies, or

(3) By creating local improvement districts in accordance with statutes governing their establishment.