4.—(1) Requesting a water undertaker to vary fluoridation arrangements is a step falling within section 89(2) of the Act if—
(a)the variation concerns the boundary of the area to which the arrangements relate, and
(b)the number of houses that would be affected by the variation, either by being brought within the area or by being excluded from it, exceeds 20% of the number of houses within the area at the time that the request is made.
(2) Maintaining fluoridation arrangements is a step falling within section 89(2) of the Act if it involves the upgrading or replacement of fluoridation plant, otherwise than for the purpose of meeting operational or health and safety standards.