From reverse osmosis systems and water conditioning systems to the plumbing used for your washing machine, an air gap is required by most local building codes in many plumbing projects. The air gap prevents contaminants from flowing back into the water system; as an example, an air gap between a wall-mounted faucet and the sink's rim requires an air gap. Air gaps, simply put, prevent back flow. Faucet Depot has a huge variety of air gaps from leading manufacturers, all ready to ship out to your door with next day shipping.