To bring about a more economical use of the available water supply, it shall be lawful for water users owning lands to which water is appurtenant to rotate in the use of the supply to which they may be collectively entitled; or a single water user, having lands to which water rights of a different priority attach, may in like manner rotate in use, when such rotation can be made without injury to lands enjoying an earlier priority, to the end that each user may have an irrigation head of at least 2 cubic feet per second.