This refers to section G3 of the Building Regulations for England and Wales which details the requirements for sanitation, hot water safety and water efficiency. The equivalent for Scotland is P3 and for Northern Ireland it is P5. It is a legal requirement for installers of domestic hot water systems to hold a G3 (or equivalent) registration to demonstrate competence in installation, commissioning, inspection and servicing. G3 (or equivalent) is recognised as a means of joining a competent person scheme to allow self-certification by the installer of the installation, which avoids the need to notify the local building control department prior to commencing work.