What backflow protection is needed for premises on a common supply?

In some cases, premises such as blocks of flats, terraced housing, caravans, holiday homes, office blocks, industrial units and student accommodation are supplied via a common supply or distribution pipe.

To prevent backflow between these separately occupied properties in addition to point of use protection the local water undertaker may require the installation of what is sometimes referred to as secondary protection. This is in effect a form of wholesite protection to protect the supplies to neighbouring properties as well as the main.

Although the level of protection required will be determined by the local water undertaker, typically a double check valve is used for this purpose.