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What Is a Dishwasher Air Gap?

A dishwasher air gap is a small but crucial device that prevents contaminated water from flowing back into your dishwasher. It ensures that your clean dishes stay sanitary by creating a physical barrier within the drainage system. Intrigued by how this simple gadget safeguards your kitchen hygiene? Discover the mechanics behind it and why it's essential for your home.
Jeremy Laukkonen
Jeremy Laukkonen

A dishwasher air gap is a component that is installed in between the drain hose of a dishwasher and a sink drain or garbage disposal. These components can be mounted into a spare sink receptacle, or through a hole drilled in a countertop. There are a few different functions that a dishwasher air gap can perform, all of which are related to the way that dishwashers drain. One purpose that an air gap can serve is to prevent water running down a sink drain from accidentally siphoning water from a dishwasher. The other purpose is to prevent sewage from ever siphoning into a fresh water supply by way of a dishwasher, which is why some local jurisdictions have building codes that require the installation of dishwasher air gaps.

Dishwashers require both a source of fresh water, and a method of draining dirty water in order to operate properly. They are typically connected into a fresh water supply for the clean water, and usually drain into the same pipe as a kitchen sink. Most garbage disposals also include a port that a dishwasher drain hose can be connected to. When a wash cycle completes, most dishwashers have a pump that is used to direct all of the dirty water into the sink drain pipe or garbage disposal.

Dishwashers require a way to funnel in clean water and drain out dirty water.
Dishwashers require a way to funnel in clean water and drain out dirty water.

In some cases, a dishwasher drain hose does not connect directly to a drain pipe or disposal. Installations such as these include an additional component, which is referred to as a dishwasher air gap. These air gaps are typically just tubes that have protective or decorative sheaths covering them, and a Y connection on the bottom side. One side of the Y connection is hooked into a dishwasher drain hose, while the other is connected to a disposal or sink drain.

The main reason to use a dishwasher air gap is to prevent a siphoning action, either out of or into a dishwasher. Without a dishwasher air gap, the drain hose of a dishwasher may act as a siphon under certain circumstances. Running water into a kitchen drain may accidentally siphon the water out of a dishwasher, preventing it from operating properly. There is also a chance of sewage entering a dishwasher if it backs up past a p-trap and into a sink drain. If this was to happen, sewage could potentially siphon all the way into the water inlet and contaminate the entire fresh water supply of a community.

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Discussion Comments


Can you explain why I have never seen an air gap to a dishwasher in Germany? I have also read that European dishwashers have air gaps (backflow preventer valves) built in. Why would their system not work in the US?

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    • Dishwashers require a way to funnel in clean water and drain out dirty water.
      By: mitev
      Dishwashers require a way to funnel in clean water and drain out dirty water.