Choosing an air gap faucet means matching it to the system behind it as well as to the sink in front of it, and systems with extra stages complicate that slightly. The faucet itself is standard; what varies is the deck hole it needs, the tubing it accepts and, on systems with remineralization, where that cartridge sits relative to the tap.
Deck hole and worktop material
An air gap faucet needs a larger hole than a plain one because its base carries three channels, and the required diameter varies by model rather than following a single standard. Measure the specific faucet's requirement against the hole you have or intend to make. Enlarging a hole in stainless is straightforward with a step drill; composite is manageable; stone is a specialist job and an expensive surprise if discovered after the box is open. Check before ordering, not after.
Tubing sizes and count
Three tubes rather than one: product water up to the spout, the reject line up into the body, and a larger gravity tube down to the drain. Confirm the faucet accepts the tubing sizes your system uses, since mixing diameters at push fittings is the classic leak that appears a day later. The gravity tube in particular should be the diameter the faucet specifies rather than something smaller that happens to fit, because that line flows without pressure and is unforgiving of restriction.
Where a remineralization stage sits
After the membrane and after any polishing carbon, so nothing downstream strips out what it has just added, which usually means immediately before the faucet. That places another inline cartridge in the run to the tap, so allow for it in the tubing layout and check clearance to change it. It also adds a small restriction, which is one more reason to keep the run short. The faucet itself does not change; only the length and content of the line feeding it does.
Finish, height and practicalities
Match the finish to the existing tap if that matters to the household, and check spout height and reach against the bowl you actually have, since a short spout over a deep sink is awkward daily. Confirm the mounting hardware suits your worktop thickness, which thick stone can defeat. And check that replacement parts are available. Our reverse osmosis with remineralization guide covers systems that include that stage.
Questions people ask about reverse osmosis faucet with air gap
Does an air gap faucet need a special hole?
A larger one, and the diameter varies by model, so measure against the specific faucet before drilling or ordering.
How many tubes does it take?
Three: product water to the spout, the reject line up into the body, and a larger gravity tube down to the drain.
Where does a remineralization cartridge go?
After the membrane and any polishing carbon, usually immediately before the faucet, so nothing removes what it has added.
Does the gravity tube size matter?
Considerably. It flows without pressure, so a smaller tube that happens to fit will cause water to appear at the gap.