Every person, firm, corporation or association engaged in the distribution and sale of natural gas for domestic use, under a franchise granted by any city having a population of 500 or more within this state, shall receive compensation for the same upon the basis of efficient and adequate service, and when such service is inefficient because of inadequate pressure the rate charged such consumers shall be graduated or reduced according to rules and regulations prescribed by the corporation commission for the state of Kansas, as hereinafter provided.
K.S.A. 66-120