Air gap faucets exist to satisfy a backflow requirement on a reverse osmosis drain connection, and whether you need one is decided by local plumbing code rather than by preference. That makes the order of decisions unusual: find out what is required first, because it changes the hole in your worktop and the plumbing behind it.
What the requirement is for
The drain line from a reverse osmosis system connects to the waste pipe, and without a break in that path a blockage or a pressure event downstream could push waste water back towards the system and, from there, towards drinking water. An air gap is a physical vertical break that makes that impossible. Many jurisdictions require it on this connection, and the requirement exists for the same reason a tap spout sits above the rim of a basin rather than below it.
Two ways to satisfy it
The faucet type carries the drain line up through its body, across an open gap, and back down to the waste, which is why it has three tubes and needs a larger deck hole. The alternative is an approved in line air gap device fitted in the drain line under the sink, which satisfies the same requirement while allowing a plain faucet with a single tube and a smaller hole. Where the faucet style is unwelcome, that second route is worth asking about before assuming you are stuck with it.
What changes if you fit the faucet type
The deck hole is larger, and the required diameter varies by model, so measure against the specific faucet rather than assuming a standard. There are three tubes to route rather than one, and the third, which carries water down from the gap to the drain by gravity, must run continuously downhill with no dips or kinks. And you should expect an audible gurgle during production, which is water crossing the open break and is normal rather than a fault.
Choosing between models
Beyond the code question, compare the finish against your existing tap, the height and reach of the spout over the bowl you actually have, and whether the manufacturer supplies the tubing sizes your system uses. Check the deck thickness the mounting hardware accommodates, since a thick stone worktop defeats some fixings. And confirm replacement cartridges and o-rings are available. Our quote page covers specifying a system and its fittings together.
Questions people ask about air gap faucets
Do I have to use an air gap faucet?
It depends on local plumbing code. Where an air gap is required, an approved in line device in the drain line is often an acceptable alternative.
Why does it need a bigger hole?
Its base carries three channels rather than one, so the deck hole is larger and the size varies by model.
Is the gurgling sound normal?
Yes. It is water crossing the open break during production, which is the design working rather than a fault.
What should I check before ordering?
The code requirement, the deck hole size for that model, the deck thickness the fixings allow, and the tubing sizes your system uses.