Air Gap vs. Non-Air Gap Faucet

What type of Reverse Osmosis Faucet Should I Buy? Air Gap vs. Non-Air Gap

There are many different makes and models of RO systems, but most install under the kitchen sink. One of the common questions we're asked, is "do I need an air gap or a non-air gap faucet?" Generally, Reverse Osmosis systems come standard with an air gap faucet but most manufacturers will also offer the non-air gap option.

Air gap faucets were designed to protect the RO system. In the event of clogging, a small amount of air, rather than dirty water, would go back into the RO system.

Both types of faucets have their advantages and disadvantages.

What's the difference between an “Air Gap” and a “Non-Air Gap” faucet?Air Gap vs. Non air-gap RO faucets

All RO systems send some water to the drain. This is due to the extremely fine nature of RO filtration. To continually produce excellent water the RO membrane (filter) continuously washes itself off and sends the impurities to the drain. The drain line from the RO membrane to the sink drain can take one of two paths: Air gap or non-air gap faucets.

When it comes to RO faucets, there are a variety of styles and finishes to choose from whether you select an air gap or a non-air gap faucet. The main difference between an air-gap and non-air gap faucet is that an Air Gap Faucet is designed to create a physical siphon break from the Reverse Osmosis (RO) system itself and the sink drain. Without getting too technical, an air gap system is where water is dropped from one tube into another through the air. This design came about so that in the event of a sink drain being clogged and backed up, the air gap installed in the RO discharge line would pull a small amount of air rather than the dirty water back into the RO unit.

With an air gap faucet, the drain line water from the RO membrane is routed up to the bottom of the faucet where it drops into a non-pressurized trough and then flows by gravity down to the sink drain. Whereas a non-air gap faucet sends the drain line water from the RO membrane directly into the sink drain. A non-air gap faucet only has the drinking water line connect to it.

Can I replace an air gap faucet with a non-air gap faucet?

Yes, you can switch out faucets. Keep in mind that an air gap faucet uses 1/4" tubing from the system to the faucet and 3/8" tubing from the faucet to the drain. A non-air gap typically uses 1/4" tubing from the system directly to the drain. To convert, simply take the 1/4" tubing from the system directly to the drain, but may need to find a fitting to reduce the connection from 3/8" to 1/4" to fit the drain line tube now coming directly from the system.

Picture of an Air Gap Faucet side by side a Non Air Gap Faucet

Air gap faucets were designed so that in the event of clogging, a small amount of air (rather than dirty water) would go back into the RO system.

The Pros and Cons of an Air Gap Faucet

Air Gap RO Faucet Advantages

Air Gap RO Faucet Disadvantages

System protection: In the event of a stopped up sink drain, the physical line break in an air-gap system ensures that water is not siphoned back into the RO system (which could damage the unit and contaminate the membrane).

Clogging: Small tubing and trough on the air-gap system can cause sediment clogging resulting in water backing up into sink or counter tops.

Plumbing Codes: In many areas the local plumbing code requires the use of an Air Gap faucet with an RO system (and air gap faucets only work with air gap RO systems).

Noisy: There’s a physical air barrier of water dropping into the trough, Air Gap faucets can make a gurgling sound while the storage tank is being filled.

 

Difficult installation: Extra tubing and connections makes the installation cumbersome.

 

Location: An air-gap system won’t work if not installed by a faucet since it must be connected to a sink drain.

The Pros and Cons of a Non-Air Gap (Regular) Faucet:

 

Non-Air Gap Reverse Osmosis Faucet Advantages:

Non-Air Gap Reverse Osmosis Faucet Disadvantages:

Lower Cost: Non-air gap systems are generally is less expensive than air gap systems.

Potential Damage: Chance that if the drain backs up, the RO system could be damaged or the membrane contaminated.

Less tubing/hoses: A non-air gap unit simply has one water line that goes up to the faucet.

Plumbing Codes: Considered non-compliant for some city/county plumbing codes.

Noise: No gurgling sound since the drain line from the RO membrane flows directly into the sink drain line.

 

Ease of Installation: Fewer connections and tubing allows for easier installation.

 

Why are Air Gap Systems Noisy?

Generally, Reverse Osmosis systems are very quiet -- though you may hear a “gurgling” sound as the “concentrate” or wastewater flows from the membrane to the drain. Reverse Osmosis is designed so that “crossflow” water flushes the contaminated concentrate away from the system. This flushing keeps the unit from fouling.

You might hear additional sounds if you have an air gap system as these systems tend to make a gurgling sound as the storage tank is being refilled. Also, as the tank is slowly filling with water, water is also slowly flowing to the drain line under the faucet. This water falls into the “air gap” trough and then flows down to the sink drain. The slow trickle of water often causes a gurgling sound.

Note that if you hear “hissing” noises, you should immediately call your local water treatment professional as there may be a problem with water pressure, the air gap, or a leak.

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Air Gap Faucets  Non-Air Gap Faucets

 

Air Gap Faucet Diagram

Non-Air Gap Faucet Diagram