The appropriation of water hereafter shall in every case be deemed and be taken to be accomplished and effectual only as to so much water as shall have been actually applied to beneficial uses within a reasonable time after the commencement of the works by means of which such appropriation is intended to be made, or afterwards where no appropriation has in the meantime been initiated by others, together with the reasonable amount necessary to supply losses by waste, seepage and evaporation; all the residue of the water within the capacity of the canal or other works shall be deemed to be derelict, and liable to appropriation by any subsequent appropriator.