When any city of the first class has approved bonds and constructed a system of waterworks and obtained an adequate supply of water but the water is turbid or unwholesome during the whole or a portion of the year, the mayor and city council may without having previously made an appropriation therefor, when authorized by a majority vote of the electors voting on the question, which may be submitted at either a special or a general city election, construct, purchase, or enter into a contract for the construction or purchase of and install, establish, operate, and maintain a system of settling reservoirs, a system of filters, or both, for the purpose of clarifying and purifying such water. Notice of such election shall be given by publication once each week three successive weeks prior thereto in a legal newspaper in or of general circulation in such city. The city may levy taxes on all taxable property of such city, not to exceed three and five-tenths cents on each one hundred dollars upon the taxable value thereof in any one year for the payment of the cost thereof.