9. In regulation 12–
(a)in paragraph (1), at the beginning insert “Subject to paragraphs (2) to (5),” and after “of samples taken” insert “for a water supply zone”;
(b)in paragraph (2), after “analysis of samples taken” insert “for a water supply zone” and at the end insert “within that zone”;
(c)after paragraph (2), insert the following paragraphs–
“(3) Subject to paragraphs (4) and (5), the Secretary of State may at any time modify or revoke an authorisation granted under paragraph (1).
(4) Unless it appears to the Secretary of State that the immediate modification or revocation of an authorisation is required in the interests of public health, he shall not modify or revoke such an authorisation without giving at least six months', or, if the water undertaker to which the authorisation relates agrees, at least six weeks', notice of his intention to do so to that undertaker.
(5) The water undertaker shall notify the Secretary of State as soon as it believes that an analysis of samples taken for a water supply zone from a point other than a sampling point would produce data in respect of the parameter in question which would be significantly different from the data produced by an analysis of samples taken from any of the sampling points within that zone; and notwithstanding paragraph (4) the Secretary of State shall thereupon revoke the authorisation.”.