13.—(1) Subject to paragraphs (2) and (4), in each year a water authority shall take, or cause to be taken, from the point at which water leaves each treatment works which serves its water supply zones, the standard number of samples for analysis–
(a)for determining the concentration of residual disinfectant;
(b)for determining whether, in relation to the colony counts and turbidity parameters, water leaving treatment works meets the specifications for those parameters set out in Schedule 2; and
(c)for testing for compliance with the prescribed concentrations or values set out in Schedule 1 in respect of the coliform bacteria, E. coli and nitrite parameters for water leaving treatment works.
(2) Where in each of two successive years the results of the analysis of samples taken, subject to paragraph (3), in accordance with these Regulations have established–
(a)in respect of the coliform bacteria, E. coli or nitrite parameter, that the maximum concentration has not been exceeded;
(b)in respect of the turbidity parameter that the specification has been met;
(c)in respect of the colony counts parameter, that there has been no significant increase,
the number of samples to be taken in respect of that parameter in the next following year from the point at which water leaves that treatment works may, subject to paragraph (4), be the reduced number.
(3) Paragraph (2) shall apply–
(a)where the following year is 2004, as if for “these Regulations” there were substituted “the 1990 Regulations”; and
(b)where the following year is 2005, as if before “these Regulations” there were inserted “the 1990 Regulations and”.
(4) In respect of the coliform bacteria parameter and the E. coli parameter, the reduced number of samples may be taken in accordance with paragraph (2) only if the water authority is of the opinion–
(a)that there is no foreseeable risk that the supply will exceed the maximum concentration for that parameter; or
(b)that the treatment works is designed to secure that, in the event of a failure of the disinfection process, water that has not been disinfected cannot enter the supply.
(5) Samples required to be taken by this regulation shall be taken at regular intervals.