18.—(1) Where a water undertaker has reason to believe that water supplied by it for regulation 4(1) purposes does not meet the specifications for indicator parameters set out in Schedule 2, it shall take such steps as are necessary to identify—
(a)the reason why the specifications are not met;
(b)the indicator parameters in respect of which the specifications are not met; and
(c)if the specification for the coliform bacteria or colony count parameter (items 4 and 5 in Schedule 2) is not met, whether the inability to meet that specification is attributable —
(i)to the domestic distribution system;
(ii)to the maintenance of that system; or
(iii)to neither of those matters.
(2) As soon as may be after the matters specified in paragraph (1) have been identified, the water undertaker shall notify the Secretary of State—
(a)of those matters; and
(b)in relation to each parameter identified in accordance with paragraph (1)(b), whether it is the opinion of the water undertaker that a recurrence of the inability to meet the specification in respect of that parameter is likely.
(3) Where, in a case to which paragraph (1)(c) applies, the inability to meet the specification has been identified as attributable to the domestic distribution system or to the maintenance of that system, the water undertaker shall, at the same time as notification is given under paragraph (2)—
(a)by notice in writing to those of its consumers—
(i)to whom it supplies water for regulation 4(1) purposes; and
(ii)who are likely to be affected,
inform them of the nature of the problem and provide details of the steps (if any) that, in the opinion of the water undertaker, it is necessary or desirable for those consumers to take in the interests of their health; and
(b)send a copy of that notice to the Secretary of State and to each appropriate local authority.
(4) Where such an inability as is mentioned in paragraph (3) is, in the opinion of the water undertaker, likely to affect the supply of water to the public in premises in which water is so supplied, it shall, at the same time as notice is given under paragraph (2), notify such persons as the Secretary of State may from time to time determine for the purposes of this paragraph of the matters of which notice is given to consumers in accordance with paragraph (3)(a).