All cities of the first class of the state of Kansas having a population of more than 100,000 inhabitants, which own, manage, operate and control a municipal electric-light plant and a municipal water plant and which are producing and distributing water, light, heat and power for domestic, industrial, commercial or municipal purposes within or without or within and without the corporate limits of said cities, are hereby empowered to place in the funds used for governmental functions of said cities, at a specified time a certain percentage of the gross operating revenue of said enumerated utilities, or either of them, as hereinafter directed: Provided, That such cities, if necessary, may adjust their utility rates in order to carry out the provisions of this act or where these utilities are managed, operated and controlled by a board of public utilities, or other managing boards, these boards shall have the power to adjust the rates.