What is the minimum air gap required for a makeup water supply above the overflow of a nonpotable water storage tank?

The minimum air gap required for a makeup water supply above the overflow of a nonpotable water storage tank is four inches. This requirement is established to prevent contamination of the potable water supply from nonpotable sources. An air gap creates a physical separation that reduces the risk of backflow, which can occur if there are fluctuations in pressure that might draw water from the tank back into the public water supply.

By maintaining a four-inch air gap, it ensures that even if there's a backflow situation, the water cannot bridge the gap and contaminate the drinking water. This standard is part of the plumbing codes established to safeguard public health, emphasizing the importance of keeping nonpotable water systems thoroughly separated from potable systems.

Other options do not provide sufficient separation, thus not adequately protecting against contamination risks. Each of them falls short of the required distance that is essential in maintaining safe drinking water standards.