23. In the case of natural mineral water, each district council must carry out periodic checks to ensure that—
(a)the composition, temperature and other essential characteristics of the water remain stable within the limits of natural fluctuation;
(b)without prejudice to subparagraph (a), the composition, temperature and other essential characteristics of the water are unaffected by any variations in the rate of flow;
(c)the viable colony count at source (before the water is subjected to any permitted treatment) is reasonably constant, taking into account the qualitative and quantitative composition of the water considered in the recognition of the water and that it continues to satisfy the requirements of Part 1 of Schedule 1; and
(d)the requirements of Schedule 4 are met in relation to the water.