When installing your potable water tank, an airgap is required to prevent backflow contamination and ensure the safe delivery of water. To satisfy the requirements for a Type AF (Fixed) or Type AG (Automatic) airgap, you can use a byelaw kit, which is specifically designed to maintain the correct gap between the water tank and any water supply.

The size of the airgap should be properly calculated and installed to prevent any potential risks. According to regulations, the airgap should be at least 1.5 times the size of the float valve controlling the water feed into your tank. 

Ensuring that the installation is done correctly and that the airgap is appropriately sized is crucial for preventing water contamination.