When water-supply to be applied to canal.

4. Whenever it appears expedient or necessary to the Government that the water of any river or stream flowing in a natural channel, or of any lake or any other natural collection of still water, should be applied or used by the State Government for the purposes of any existing or projected canal, the State Government may, by notification in the Official Gazette, declare that the said water shall be so applied or used after such date as may be specified in the said notification, not being earlier than three months from the date thereof.