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What Is a Dishwasher Air Gap? And Why You Might Need One

AZpartsA
AZparts Team
Updated on July 10, 2025
9 min read
Have you ever wondered what is dishwasher air gap is and why it’s important? The air gap is a small but crucial device that prevents dirty water from flowing back into your clean water supply, ensuring your dishwasher operates safely and hygienically. In this article, AZParts explains what an air gap is, how it works, and why every dishwasher should have one.
what-is-dishwasher-air-gap

1. What is a Dishwasher Air Gap?

A dishwasher air gap is a small yet essential plumbing device installed above the sink or countertop, typically near the faucet. Its primary function is to prevent contaminated water from flowing backward into the dishwasher during drainage. By creating a physical break in an open gap of air between the dishwasher's drain hose and the household plumbing, it ensures that dirty water from a clogged sink or garbage disposal cannot be siphoned back into the appliance.

This air space acts as a fail-safe, much like the space between a kitchen faucet and the sink rim, which stops sink water from reaching the faucet in case of overflow. In short, the dishwasher air gap serves as a critical safeguard for your home's potable water supply, keeping your dishwasher and your dishes free from backflow contamination.

2. How Does a Dishwasher Air Gap Work?

A dishwasher air gap is a simple but essential backflow prevention device that protects your dishwasher and clean water supply from contamination. It works by creating a physical space of air between two hoses:

  • From Dishwasher to Air Gap : Dirty water is pumped out of the dishwasher through the first hose, which rises to the air gap fitting.
  • From Air Gap to Drain : The water flows through the air gap and into a second hose that leads to the garbage disposal or drain.
This air break prevents dirty water from siphoning back into the dishwasher if the drain becomes clogged or pressure changes occur. Installed on your sink or countertop, the air gap's visible cap also serves as an overflow outlet; if water leaks from it, it signals that your dishwasher did not drain, which the blockage needs to be cleared.

it-functions-by-forming-an-air-gap-between-two-hoses-source-azparts
It functions by forming an air gap between two hoses (Source: AZParts)

3. What Is the Purpose of a Dishwasher Air Gap?

The dishwasher air gap prevents contaminated water from re-entering the dishwasher by blocking backflow. It ensures that once dirty water is pumped out, it’s directed safely to the drain or garbage disposal, never back into the appliance. This protects both your dishwasher and your dishes, maintaining hygiene and preventing cross-contamination during every wash cycle.

4. Is a Dishwasher Air Gap Necessary?

Yes, especially if you want reliable backflow protection. In many states like California, Washington, and Minnesota, air gaps are legally required by plumbing codes for residential dishwashers. They’re the only method that guarantees prevention of contaminated water re-entering your dishwasher, regardless of drain clogs or pressure changes.

While alternatives like high loops or check valves exist, they can fail. Air gaps have no moving parts and rely on simple physics, water can’t flow backward through an open air break. If you're installing a new dishwasher or planning to sell your home, having an air gap ensures both compliance and protection.

5. Where Is the Dishwasher Air Gap Located?

The dishwasher air gap is usually installed on the sink deck or countertop, right beside the kitchen faucet. It appears as a small chrome or stainless steel cylinder, often mistaken for a soap dispenser or extra faucet.

Beneath the surface, the air gap connects two hoses: one runs from the dishwasher to the air gap, and the other leads from the air gap to the sink drain or garbage disposal. This setup creates a physical air break that prevents dirty drain water from backing up into the dishwasher. Though small and often overlooked, the air gap plays a critical role in protecting your dishwasher and ensuring your dishes stay clean.

the-air-gap-sits-next-to-the-kitchen-faucet-on-the-sink-or-counter-source-azparts
The air gap sits next to the kitchen faucet on the sink or counter (Source: AZParts)

6. Do New Dishwashers Need an Air Gap?

Whether a new dishwasher needs an air gap depends on local plumbing codes and how the drain hose is installed. In many states such as California, Washington, and Hawaii—air gaps are required by law for all dishwashers, regardless of brand or age. If your drain connection is lower than 20 inches from the floor, an air gap is typically necessary to prevent backflow.

So what do you need to install a dishwasher? Some newer dishwashers include built-in backflow prevention features or recommend the high loop method (routing the drain hose up beneath the counter). While this can reduce the risk of contamination, it isn’t always up to code. Built-in or alternative solutions may help, but only a countertop air gap is universally accepted by inspectors in regulated areas. Always check your local plumbing requirements before installation.

7. How to Install a Dishwasher Air Gap

Installing a dishwasher air gap is a straightforward DIY project that helps prevent backflow and keeps your dishwasher functioning properly. Here's a step-by-step guide:

1. Check for a Countertop Hole:  Most sinks come with a pre-drilled hole near the faucet for an air gap. If not, you’ll need to drill a 1-3/8” hole close to the sink rim. Use masking tape around the area to avoid scratches. For granite or stone counters, consider hiring a professional.

2. Prepare Materials: You’ll need:
  • A dishwasher air gap fitting
  • 5/8" and 7/8" drain tubing
  • Hose clamps
  • Screwdriver and adjustable wrench
3. Connect the Dishwasher Hose: Attach the dishwasher’s drain hose to the smaller (5/8") inlet on the air gap. Secure it with a hose clamp.

connect-the-dishwasher-drain-hose-to-the-air-gap-inlet-source-azparts
Connect the dishwasher drain hose to the air gap inlet (Source: AZParts)

4. Connect to Drain or Garbage Disposal: Attach a 7/8" hose to the larger outlet on the air gap. This hose runs to either the garbage disposal or a Y-branch tailpiece on your sink drain. Use hose clamps to ensure tight, leak-free connections.

Important: If connecting to a disposal that hasn’t had an air gap before, knock out the plug inside the inlet first.

5. Mount the Air Gap: Insert the air gap up through the hole in the counter from below. Secure it with the mounting nut, then snap the decorative cap into place. Have someone hold it steady while tightening to prevent it from turning.

6. Test the Installation: Run your dishwasher through a fill or rinse cycle. Check all connections for leaks and ensure water flows freely through the hoses and down the drain. With proper installation, your air gap will provide lasting protection against backflow, no moving parts, just simple physics doing its job.

8. Should Water Come Out of the Dishwasher Air Gap?

No, under normal conditions, water should not come out of the dishwasher air gap. If you see water leaking or spilling from it, it usually means there's a clog in the drain hose between the air gap and the garbage disposal or sink drain. This blockage causes wastewater to back up and escape through the air gap's vent holes.

While it may look alarming, the leak is actually a safety feature, it prevents dirty water from flowing back into your dishwasher. Try clearing the hose or cleaning out the air gap to restore proper drainage. If the issue persists, professional plumbing assistance may be needed.

water-dont-come-out-of-the-dishwasher-air-gap-source-azparts
Water don’t come out of the dishwasher air gap (Source: AZParts)

9. How to Clean or Unclog a Dishwasher Air Gap

If water is leaking from your dishwasher air gap, it likely means there’s a clog that needs clearing. Here’s how to clean or unclog it:

1. Remove the Cover: Take off the decorative cap from the air gap on your countertop to access the opening.

2. Clean with a Bottle Brush: Use a long-handled bottle brush to scrub inside the air gap and dislodge any food debris or buildup from the tubing.

3. Dislodge Debris Manually: For light blockages, you can place a cardboard tube (like a paper towel roll) over the air gap opening and blow firmly to push out any obstruction.

4. Check the Garbage Disposal Plug: If your garbage disposal was recently installed, a common issue is that the knockout plug inside the air gap inlet wasn’t removed.
  • Unplug the disposal and disconnect the drain hose from the air gap.
  • Use a screwdriver and hammer to gently knock out the plug.
  • Reconnect the hose, then reach inside the disposal to remove the loose plug piece before restoring power.
5. Run a Test Cycle: Once everything is reconnected, run the dishwasher and check for leaks or drainage problems. Regular cleaning of the air gap helps prevent clogs and ensures your dishwasher drains properly.

cleaning-a-dishwasher-air-gap-is-the-most-important-ways-to-fix-leaking-issue-source-azparts
Cleaning a dishwasher air gap is the most important ways to fix leaking issue (Source: AZParts)

10. FAQs about what is dishwasher air gap

10.1. Can I install a dishwasher air gap under the counter?

No . A dishwasher air gap must be installed above the sink or countertop to work properly. Its elevated position ensures a physical break in the water path, which prevents backflow. Installing it under the counter defeats its purpose and violates plumbing code.

10.2. Is it okay to remove the dishwasher air gap?

Only if your local plumbing code allows it. In many regions, especially in states like California or Washington, air gaps are legally required for dishwashers. Even if not mandated, removing the air gap can expose your dishwasher to the risk of backflow and contamination.

10.3. Do all dishwashers need an air gap?

Not all, but many do —especially in areas where building codes require it. If an air gap isn’t required, some homeowners use the high loop method (routing the drain hose high under the sink). However, an air gap is the most reliable and code-compliant way to prevent dirty water from entering your dishwasher.

While often overlooked, a dishwasher air gap is a key component in maintaining a safe and efficient kitchen. It prevents contaminated water from flowing back into your appliance, protecting both your dishes and your home’s water supply. Whether required by local code or added as a precaution, an air gap offers peace of mind and reliable backflow protection.

If you're upgrading or repairing your dishwasher, be sure to choose quality components. From air gaps to hoses and fittings, AZParts provides a wide range of dishwasher parts which fit various models as Crosley Dishwasher Parts, Kenmore Dishwasher Parts… to help keep your appliance running smoothly and safely.

Contact Information:
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