It shall be the duty of every water undertaker or water supply licensee to promote the efficient use of water by that person's customers.
The duty of a water undertaker or water supply licensee under this section shall be enforceable under section 18 above—
by the Secretary of State; or
with the consent of or in accordance with a general authorisation given by the Secretary of State, by the Authority.
Nothing in this Part shall have effect to authorise or require a water undertaker or water supply licensee to impose any requirement on any of that person's customers or potential customers.