5.—(1) Any product or substance used in the preparation or distribution of a private supply of water, or impurities associated with such products or substances, must not be present in water at the point of use at levels that would make it unwholesome or constitute a potential danger to human health.
(2) Where disinfection forms part of the preparation or distribution of water, the relevant person must—
(a)design, operate and maintain the disinfection process so as to keep disinfection by-products as low as possible without compromising the effectiveness of the disinfection,
(b)ensure that the effectiveness of the disinfection process is maintained, and
(c)verify the effectiveness of the disinfection process.