21.—(1) Subject to paragraph (3), where an investigation under regulation 17(1) establishes that the failure in question is on-going and constitutes a potential danger to human health, Scottish Water must take such action as is necessary to protect human health from that danger (such as isolating anything that appears to be affecting, or may affect, the quality of the water).
(2) Scottish Water must decide what action should be taken to comply with paragraph (1), bearing in mind the risks to human health which would be caused by an interruption of the supply or a restriction in the use of water intended for human consumption.
(3) Where the investigation establishes that the failure is due to a domestic distribution system in premises where water is supplied to the public (or to the maintenance of that system), paragraph (1) does not apply in so far as a local authority must, under section 76FB of the 1980 Act, require the person who owns or is otherwise responsible for that system to take any such action as is required by that paragraph.
(4) Scottish Water must inform (in so far as it has not already done so) those of its consumers who are likely to be affected by the failure of any action taken under paragraph (1).