The mayor and city council shall have power to borrow money and pledge the property and credit of the city upon its negotiable bonds or otherwise in an amount not exceeding in the aggregate four hundred thousand dollars for the purpose of constructing or aiding in the construction of a system of sewerage. The city may borrow money and pledge the property and credit of the city upon its negotiable bonds or otherwise in any amount, not exceeding in the aggregate seven hundred fifty thousand dollars, for the purpose of constructing culverts and drains for the purpose of deepening, widening, straightening, walling, filling, covering, altering, or changing the channel of any watercourse or any natural or artificial surface waterway or any creek, branch, ravine, ditch, draw, basin, or part thereof flowing or extending through or being within the limits of the city and for the purpose of constructing artificial channels or covered drains sufficient to carry the water theretofore flowing in such watercourse and divert it from the natural channel and conduct the water through such artificial channel or covered drain and fill the old channel. The city may borrow money and pledge the property and credit of the city upon its negotiable bonds or otherwise in an amount not exceeding in the aggregate two hundred fifty thousand dollars for the purpose of constructing, maintaining, and operating a system of waterworks for the city. No such bonds shall be issued by the city council until the question of issuing the bonds has been submitted to the electors of the city at an election called and held for that purpose, notice of which shall be given by publication in a legal newspaper in or of general circulation in the city at least thirty days before the date of the election, and a majority of the electors voting upon the proposition have voted in favor of issuing such bonds. When any such bonds have been issued by the city, the city may levy annually upon all taxable property of the city such tax as may be necessary for a sinking fund for the payment of the accruing interest upon the bonds and the principal thereof at maturity. The city may provide for the office of sewer commissioner or water commissioner and prescribe the duties and powers of such offices.