The choice between an air gap and a non air gap faucet is a choice about how the reverse osmosis system gets rid of its reject water. One breaks the drain path with open air inside the faucet body; the other runs a single tube to the drain saddle. Both are sold everywhere, and the decision usually comes down to your local code and how much noise you will tolerate.
The practical differences you will live with
A non air gap faucet is quieter, needs only one small tube up to the deck, fits a standard soap dispenser hole and is far simpler to install. An air gap faucet gurgles while the system produces, needs a bigger hole and three lines under the sink, and has a vent slot at its base that can spit if the drain line ever partly blocks. Against that, the air gap version physically cannot allow sink waste to be drawn back toward the unit, and that is the only argument that really matters.
What your code and your sink decide for you
Plumbing requirements vary by jurisdiction, and some inspectors will insist on an air gap for any point-of-use treatment unit discharging to a drain. Check before you buy, because retrofitting later means enlarging a hole in a stone or composite sink deck, which is not a five-minute job. The sink itself has a vote too: a small hole count, a thick counter or a garbage disposal on the same tailpiece can all push the decision one way before preference gets a look in.
The honest recommendation
If code allows it and the drain saddle sits properly above the trap, most households are happier with the quieter non air gap faucet and never think about it again. Choose the air gap version where code requires it, where the drain connection has to sit low, or where you simply want the physical break. Neither choice changes the water you drink by one bit: they differ only in how waste leaves. Our best faucet water filter guide covers the case where you do not need reverse osmosis at all.
Questions people ask about air gap vs non air gap faucet
Is a non air gap faucet unsafe?
In normal operation, no. The air gap exists to protect against an unusual failure, a backflow or siphon from the drain, which a plain tube could in theory allow and a gap of air cannot.
Why does my air gap faucet spit water at the base?
The drain line is restricted, often at the saddle or by debris, so reject water backs up and escapes through the vent. Clear the line rather than blocking the vent.
Can I swap an air gap faucet for a non air gap one later?
Usually yes, and it is the easier direction to go since the hole is already large enough. Cap the redundant drain saddle port properly when you do.