These measures result from the Water Supply (Water Fittings) Regulations 1999 (‘the Regulations’), as they apply in England and Wales, and regulate how water systems are designed, installed and operated. The Regulations require water fittings to be an appropriate quality and standard and suitable for the circumstances in which they are used. To meet these requirements, Regulator Specifications can be approved to provide detailed performance characteristics to ensure, amongst other things, that a fitting will not cause contamination of the water supply thereby protecting human health. These measures amend the Regulator Specifications that relate to: the design and performance of Water Closet suites and their components; backflow prevention arrangements and their classifications; and, relevant testing requirements. The amendments, to prevent water from a Water Closet cistern backflowing into a clean drinking water supply, will: introduce a new backflow prevention arrangement for Water Closets; and, apply appropriate testing requirements. Regulator Specifications are relevant to the compliance of certain water fittings in Scotland with the Water Supply (Water Fittings) (Scotland) Byelaws 2014 and in Northern Ireland with the Water Supply (Water Fittings) Regulations (Northern Ireland) 2009.