Reverse Osmosis Air Gap – What Is It and How Does It Work?

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Reverse osmosis air gaps and air gap RO faucets provide added protection to your home’s drinking water supply against contamination from bacteria and certain other contaminants.

But what is a reverse osmosis air gap exactly, and how does it work?

Let’s find out!

Key Takeaways

  • A reverse osmosis air gap is a mechanism within your RO air gap faucet.
  • It is used to keep water moving through the proper drains the right way so contaminated water doesn’t backflow to your reverse osmosis system and contaminate it.

What Is a Reverse Osmosis Air Gap?

A reverse osmosis air gap is a specific type of plumbing component that is used to prevent contamination of your reverse osmosis system and ultimately your RO drinking water.

The air gap is literally a gap or hole in your RO system’s drain line. This hole is built into the base of reverse osmosis faucets, making them air gap RO faucets.

The Purpose

The purpose of a reverse osmosis air gap is to make sure that no water from a blocked sink can siphon backward into your reverse osmosis system, thus preventing the system from potential contamination.

The air gap keeps the water flowing the right way, as water cannot climb air, and therefore it stops any unused filtered water that has traveled back your RO system’s drain line from backwashing into the unit itself causing contamination.

plumber installing reverse osmosis system under sink

How Does an Air Gap RO Faucet Work?

An air gap RO faucet has three lines, one for carrying filtered water, one for the drain water to be carried up, then it passes the air gap and drops into a third tube headed downwards to be disposed of as wastewater via your sink’s drainpipe.

If any wastewater travels from the drain pipe’s drain saddle up the drain line, due to a blockage, it won’t be able to move past the air gap.

Advantages and Disadvantages of Reverse Osmosis Air Gap Faucets

Air gap RO faucets come with a few advantages and disadvantages worth mentioning, which are important to consider when deciding whether to go with an air gap faucet or a non-air gap faucet.

No Wastewater/Sewerage Backflow

The air gap prevents wastewater or sewerage from traveling into your RO unit and contaminating it.

Plumbing Code Compliant

Some areas require an air gap reverse osmosis faucet by plumbing code.


Air gap RO faucets are not known for being quiet. They can make quite a bit of gurgling and noise.


If the drain line is blocked, water can flow out of the air gap onto your countertop or sink. This is not a rare occurrence. RO air gap faucet lines are small, so they can become blocked easily.

Extra Work

Installing an air gap RO faucet is more difficult than installing a non-air gap faucet, as they have three tubes instead of one. This means the hole you need to drill in your kitchen sink will need to be larger, too.

Air Gap vs Non-Air Gap RO System Faucets

The primary difference between air-gap and non-air gap RO faucets is in the name…one has an air-gap mechanism, and one does not. Non-air gap faucets come with just one tube instead of three and do not prevent the possibility of backflow of contaminated water to your RO unit – that’s what check valves are used for.

Usually, non-air gap faucets are cheaper and easier to install, but there is a chance they will not comply with your local plumbing codes, so that is something you’ll need to look into when you are deciding which faucet to go with.

Can You Switch Between Air Gap and Non-Air Gap RO Faucets?

It is possible to change your air gap for a non-air gap RO faucet and vice versa, as long as you aren’t violating local plumbing codes. When doing so, it is essential to remember that an air gap faucet needs ⅜ inch tubing to connect to the drain saddle, and non-air gap faucets use ¼ inch. Therefore, you might need an adapter.

If you have any questions about reverse osmosis air gaps please don’t hesitate to leave a comment below!

About the Author Gene Fitzgerald

Gene Fitzgerald is one of the founders of BOS and currently head of content creation. She has 8+ years of experience as a water treatment specialist under her belt making her our senior scientist. Outside of BOS, Gene loves reading books on philosophy & social issues, making music, and hiking.
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