Any water fitting, which when installed, will carry or receive water from the public mains water supply in the UK, must comply with the Water Supply (Water Fittings) Regulations or Scottish Byelaws. These require that a water fitting should not cause waste, misuse, undue consumption or contamination of the water supply and must be ‘of an appropriate quality and standard’.
WRAS Approval is the easiest way to demonstrate compliance as it is granted directly by representatives of the water suppliers and is therefore accepted by every water supplier in the UK.
WRAS Product Approval: Whole products such as valves, boilers & showers undergo mechanical and water quality testing. This type of approval demonstrates full compliance with requirements of the regulations and byelaws, provided the fitting is installed according to any conditions given with the approval.
WRAS Material Approval: Non-metallic materials & components, such as rubber sheet material & ‘O’ rings, undergo testing only for their effects on water quality. This type of approval demonstrates that the non-metallic material/component does not itself contaminate the water and therefore satisfies this particular requirement of regulations and byelaws.
Where do the regulations apply?
The Regulations are typically in effect between the boundary of a property and the point of discharge as illustrated below.
Source: WRAS What is a WRAS Approval?
Source2 : WIKI