Byelaw 30 kits and Byelaw 60 kits consist of a set of components designed to protect the water in a cistern from contamination. They are intended for potable water cisterns, such as the cold water storage cistern in the loft. Byelaw 30 kits often come with new cisterns. However, they can be purchased separately if one is looking to upgrade an existing installation. The main difference between the two kits is the diameter of the overflow. The Scottish Byelaw 60 stipulates a larger diameter overflow.
The kits generally consist of a screened overflow pipe, an overflow dip tube, a rubber grommet for the expansion/vent pipe, and a breather fitting. Along with the cistern lid, they are vital in keeping the water in the cistern free from dirt and debris.