What is the required type of protection between a potable water system and a building sewer?

The required type of protection between a potable water system and a building sewer is an air gap separation. This method is essential because it provides a physical barrier that prevents any potential contamination from the sewer from entering the potable water supply. An air gap is created by ensuring there is a vertical space between the highest point of the water in the plumbing system and the flood level of the sewer system, effectively eliminating any possible backflow.

The air gap is considered one of the most reliable methods of cross-connection control. It does not rely on mechanical parts, which can fail, and thus offers a long-lasting and maintenance-free solution to prevent contamination. This level of protetion is particularly important in scenarios where the risk of backflow may be high due to pressure changes in the plumbing system or in the building sewer.

Other protection methods, such as backflow preventers, atmospheric vacuum breakers, and reduced pressure zone devices, are also vital in various situations but are not suitable for use directly between potable water and a building sewer due to the unique risks involved. An air gap is the preferred method in this context to uphold health and safety standards for drinking water.