A pan for a water heater shall not be less than ____ inches in depth.

The correct answer indicates that a pan for a water heater must have a minimum depth of 1 1/2 inches. This specification is crucial for ensuring that any water or leaks from the heater are adequately contained within the pan, preventing potential damage to surrounding structures or flooring. A depth of at least 1 1/2 inches is designed to provide sufficient capacity to hold an appropriate volume of water in case of a failure.

The choice of 1 1/2 inches is based on industry standards to ensure effective drainage and safety. If a pan were to be shallower than this minimum depth, it might not effectively prevent overflow, leading to water damage or hazardous conditions. Therefore, adhering to this minimum requirement ensures that plumbing installations meet safety regulations and function as intended.