In fixing the rates at which water shall be furnished, the board of commissioners shall take into consideration the cost of the works, the expense of keeping the same in repair, and all other conditions that affect the cost of delivering the same. Whenever it shall appear to the board of county commissioners from competent evidence that any consumer or consumers of water distributed through any ditch or canal, is entitled to the distribution or use of any water therefrom, at not to exceed a proportionate amount of the actual cost of maintenance and operation of said ditch or canal, they shall, upon request of such person or persons so entitled, fix the rate per cubic foot per second to be charged to such consumer or consumers for the current year.