11.—(1) Subject to paragraph (2), where an enforcing authority has carried out a risk assessment, it must review and, where necessary, update the risk assessment at least every 5 years (or earlier if it considers that the existing risk assessment is inadequate for any reason).
(2) The enforcing authority must review and, where necessary, update the risk assessment as soon as possible in the event that it becomes aware of any—
(a)deterioration of the quality of the water;
(b)increase in the pollution of a body of water or other source used for the abstraction of the water; or
(c)modification to, or extension of, the supply system from which the water is supplied,
which is relevant for the protection of human health and was not previously taken into account.