PART 4WATER QUALITY STANDARDS AND DUTIES
Duty of care: substances and materials17
A person who, in relation to a supply of water, modifies any part of a private water supply system or introduces any substance to the water supplied (for purposes in connection with the distribution or preparation of the water) must ensure that no substance or material used or introduced for those purposes (or any impurity associated with any such substance or material)—
a
remains in the water (including, in particular, at the point of compliance) in concentrations higher than is necessary for the purpose of their use; or
b
reduces the protection of human health otherwise provided for by these Regulations.