Answer:
The number of air gaps required for a sink depends on the specific plumbing codes and regulations of your area. Generally a sink should have at least one air gap but two may be required in certain circumstances.
An air gap is a physical space or device that prevents the backflow of contaminated water into the clean water supply. It is typically installed between a sink's drain and the plumbing system to ensure the integrity of the potable water supply.
In many cases a single air gap device installed at the sink's drain outlet is sufficient to meet plumbing requirements. However there are situations where additional air gaps may be necessary. For example if your sink is connected to a dishwasher you may need a separate air gap specifically for the dishwasher discharge line. This additional air gap ensures that any potential contaminants from the dishwasher's wastewater are not able to flow back into the sink or water supply.