6. Whenever it appears expedient to the Government that the water of any river or stream flowing in a natural channel, or of any lake or other natural collection of still water, should be applied or used by the Government for the purpose of any existing or projected canal, the Government may, by notification in the official Gazette, declare that the said water will be so applied or used after a day to be named in the said notification, not being earlier than three months from the date thereof.