Whenever the commission shall find, after a hearing had upon its own motion, or upon complaint, that the rates or charges demanded, exacted, charged or collected by any gas company, electrical company, wastewater company, or water company, for gas, electricity, wastewater company services, or water, or in connection therewith, or that the rules, regulations, practices or contracts affecting such rates or charges are unjust, unreasonable, unjustly discriminatory or unduly preferential, or in any wise in violation of the provisions of the law, or that such rates or charges are insufficient to yield a reasonable compensation for the service rendered, the commission shall determine the just, reasonable, or sufficient rates, charges, regulations, practices or contracts to be thereafter observed and in force, and shall fix the same by order.