4.—(1) Subject to paragraph (2) below, every local authority shall ensure that collecting systems which satisfy the requirements of Schedule 2 are provided–
(a)where the urban waste water discharges into receiving waters which are a sensitive area, by 31 December 1998 for every agglomeration with a population equivalent of more than 10,000;
(b)without prejudice to sub-paragraph (a) above–
(i)by 31 December 2000 for every agglomeration with a population equivalent of more than 15,000; and
(ii)by 31 December 2005 for every agg lomeration with a population equivalent of between 2,000 and 15,000.
(2) Paragraph (1) above shall not apply where either–
(a)the river purification authority within whose area the discharges are made has certified that the establishment of a collecting system is not justified because it would produce no environmental benefit; or
(b)the Secretary of State has certified that the establishment of a collecting system is not justified because it would involve excessive cost,
and individual systems or other appropriate systems are provided and the river purification authority has certified that they achieve the same level of environmental protection.
(3) Every local authority shall ensure that urban waste water entering collecting systems is, before discharge, subject to treatment provided in accordance with regulation 5 and that–
(a)plants built in order to comply with that regulation are designed (account being taken of seasonal variations of load), constructed, operated and maintained to ensure sufficient performance under all normal local climatic conditions;
(b)treated waste water and sludge arising from waste water treatment are re-used whenever appropriate; and
(c)disposal routes for treated waste water and sludge minimise the adverse effects on the environment.