4. Requesting a water undertaker to vary fluoridation arrangements is a step falling within section 89(2)(b) of the Act if—
(a)the variation concerns the boundary of the area to which the fluoridation 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.