What is an air gap on a sink?

Author: Prof. Hollie Goldner IV  |  Last update: Friday, July 10, 2026

An air gap, as related to the plumbing trade, is the unobstructed vertical space between the water outlet and the flood level of a fixture. Air gaps of appropriate design are legally required by water health and safety regulations in many countries.

How do I know if my sink has an air gap?

The space between your kitchen faucet and the rim of your kitchen sink is a perfect demonstration of an air gap. If your garbage disposal is clogged and your sink overflows with filthy water, the water will spill over the rim of the sink and onto the counter.

Can I use a sink drain without an air gap?

While it's technically possible for a sink to drain without a vent, it's not recommended if you are wanting your sink drain to perform optimally. Building codes typically require proper venting to ensure the safety, efficiency, and longevity of the plumbing system.

Is an air gap faucet necessary?

Disadvantages of Non-Air Gap RO Faucets:

Without the air gap, there is a higher risk of cross-contamination if there is a problem with the plumbing system. Not Code Compliant in Some Areas: Depending on where you live, local plumbing codes may require the use of an air gap faucet with an RO system.

What happens if you don't install an air gap?

What If My Dishwasher Has No Air Gap? Without a dishwasher air gap, contaminated water can flow back into the dishwasher. A dishwasher air gap prevents this from happening by ensuring that the water flows in one direction: out of the dishwasher and into the garbage disposal.

Dishwasher Leaking Water Under Kitchen Sink: Replacing an Air Gap

What if my sink doesn't have an air gap hole?

If your sink lacks an available hole for installing an air gap, a plumber can usually drill an opening where needed.

Is a sink air gap necessary?

It creates a separation between the water supply and potentially contaminated water in a sink or other plumbing fixture. The use of an air gap is required by plumbing codes for certain plumbing fixtures, such as dishwashers, to prevent the backflow of potentially contaminated water into the clean water supply.

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

You can easily switch out faucets. Keep in mind that an air gap faucet uses 1/4" tubing from the reverse osmosis 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 RO system directly to the drain.

Do you really need an air gap?

A drain hose that is connected to house plumbing lower than 20 inches above the floor will need an air gap. Check your local codes and requirements. Unless mandated, dishwasher air gaps are not always recommended by professionals.

Does a 3 compartment sink need an air gap?

Three compartment sinks should have TWO AIR GAPS.

Can I use a high loop instead of an air gap?

Both the high loop and air gap methods serve the same purpose of preventing wastewater backflow and are commonly required by building codes to ensure the safe operation of dishwashers. The specific requirements may vary depending on your location and local plumbing codes.

What happens if a sink is not vented?

When drain lines aren't properly vented, low pressure inside the pipe can suck water out of the traps, letting sewer gas in. Air pressure imbalances inside the drain pipe can restrict water flow and cause sluggish draining, often mimicking a partial clog inside the pipe.

What is the problem with the air gap?

The most common issue with air gaps is a blockage somewhere along the line, usually due to bits of food and grease accumulating over some time. These kinds of blockages are most likely to be found in the hose between the air gap and drain/disposal (where there's less pressure to move things along).

What is the little thing next to the faucet?

The metal thing in question is a small, cylindrical metal tube that sits next to the faucet on your kitchen sink. Reddit user @dominostracker wondered the exact same thing, and according to a few wonderful human beings who took the time to answer, that thing is an air gap.

Does every sink have an air gap?

Most states even enforce plumbing codes that require dishwasher air gap installation in residential and commercial sinks. If your drain hose is connected to house plumbing lower than 20 inches above subfloor or floor you will need to use an air gap.

How do I find the air gap in my sink?

The air gap is a chrome plated cylinder located on the back of the sink where the faucet is located.

Does water come out of an air gap?

Water leaking from an air gap in an RO system may result from improper installation or a restriction preventing water from flowing to the drain. Gravity is the only force that moves water from the air gap to the drain, so any resistance causes the water to back up and leak from the air gap hole.

How much does it cost to install an air gap?

How much does a Air Gap cost? A typical price for a Air Gap is $25 but can range from approximately $6 to $41.

What is the air gap rule?

An air gap between the water supply inlet and the flood level rim of the plumbing fixture, equipment, or nonfood equipment shall be at least twice the diameter of the water supply inlet and may not be less than 25 millimeters (1 inch).

Why is the air gap so important?

As the world moves increasingly online, air gap backups provide a last line of defense against data loss. Businesses of all sizes can benefit from air gap backups, which protect data from being destroyed, accessed, or manipulated in the event of a network intrusion or system failure.

What does an air gap look like?

The air gap resembles a short, squaw cylinder that may appear to have open valves on one or both of its sides. Your sink faucet sits several inches higher than your sink rim to protect against sink water overflowing to the point that it could re-enter the faucet line where your clean water comes from.

Do I need an air gap if I have a garbage disposal?

They rely solely on basic physics and gravity to do their job. If you have a garbage disposer and a dishwasher, you will definitely want to use an air gap.

Does every sink need its own vent?

Plugged at the U-pipe, the fresh water blocks sewer gases and lets them harmlessly leak out the plumbing vents. Every plumbing fixture needs to have a vent to work properly.

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