The Secretary of the Interior in connection with the operations under the reclamation law is authorized to enter into contract to supply water from any project irrigation system for other purposes than irrigation, upon such conditions of delivery, use, and payment as he may deem proper: Provided, That the approval of such contract by the water-users’ association or associations shall have first been obtained: Provided, That no such contract shall be entered into except upon a showing that there is no other practicable source of water supply for the purpose: Provided further, That no water shall be furnished for the uses aforesaid if the delivery of such water shall be detrimental to the water service for such irrigation project, nor to the rights of any prior appropriator: Provided further, That the moneys derived from such contracts shall be covered into the reclamation fund and be placed to the credit of the project from which such water is supplied.