CAT5 compliant water booster pumps are designed to provide protection against back contamination of the water system caused by harmful waste/pathogens. The official definition of the water categories is available at legislation.gov.uk.
For over 20 years now it has been a legal requirement for CAT5 compliance, when water pumps are used in wash down applications or other high contamination risk environments.
Water pump usage, where there are risks of contamination, such as wash-down applications, have been subject to CAT5 compliance regulations for over 20 years.
Similar applications include: wash-down for bin-stores, vehicle washing, school laboratory water supplies, abattoir cleaning, hose pipes, outdoor taps at farms etc…
The protection against contamination is achieved by separating the incoming mains water supply from the boostable water, using an air-gap within a water tank. Water is supplied to the float-valve at the top of the tank and falls down into the tank itself. The float valve then shuts off the water when the level raises to a pre-set level, creating the air gap between the tank water level and the inlet. A correctly designed system also has weirs that allow water to overflow out of the tank on the extremely rare occasion the inlet valve might fail in the open position (shown as ‘Safety Gap’ in the diagram). This ensures that no matter what happens the air gap in maintained and the mains water system is protected from contamination.
Example CAT 5 Air Gap
The full version of the legislation is available here: https://www.legislation.gov.uk/uksi/1999/1148/contents/made