In case the volume of water in any canal, reservoir or other works or in case the volume of power or fuel in any district shall not be sufficient to supply the continual wants of the entire district and all lands susceptible of irrigation therein, then it shall be the duty of the board of directors to distribute all available water, power or fuel upon certain or alternate days to different users or localities, as they may in their judgment think best, for the interest of all parties concerned, provided, however, that power or fuel for the production of power shall be first served to the fullest extent practicable for use in pumping of water for irrigation.