What Is the Thing Next to My Kitchen Faucet?

When you buy a new home or move into a rental, you aren’t always familiar with all the amenities. So when you go into the kitchen, you might wonder “What is that thing next to my faucet?” You push it down, but no soap comes out, and you can’t remove it, so it isn’t a spray hose. But if you spot one of these things mounted on the kitchen sink, one thing is certain: You have a dishwasher, even if you haven’t used or even noticed it yet.

This gizmo is called an air gap, which seems a strange name for a dome-shaped metal protuberance that looks like an R2D2 mini-me. Once you understand what it does, though, you’ll see that the name is appropriate. In this post, we’ll make it make sense.

What Is the Thing Next to My Faucet?

The air gap isn’t part of your faucet, it’s part of the sink drain. Specifically, it’s part of the dishwasher drainage system. It’s there for two reasons. One to ensure that the water that the dishwasher pumps out after the wash and rinse cycles goes down the drain, and the other is to prevent water flowing back from the drain to the dishwasher in the event of a sink clog. If the dishwasher drainage system backs up, the dishwasher may stop working, and if it doesn’t, the backflow could contaminate your clean dishes. The air gap prevents that.

What Is an Air Gap?

California-based plumber Alex Atkinson explains the air gap this way: “The air gap creates a physical break between the dishwasher and the drain. That way, if your sink gets clogged and water starts backing up, it can’t siphon back into the dishwasher.”

How does it do this? If you look at it closely, you’ll notice that it has holes through which air and water can pass (you may have to remove the dome-shaped cover to see this). That’s why it’s called an air gap.

What Does an Air Gap Do?

The dishwasher drain hose stretches under the sink cabinet from the dishwasher to the sink drain, where it tees into the drain tailpiece (or the garbage disposal, if you have one). When the dishwasher’s drain cycle starts, a pump expels water through this hose, and the water pushes a layer of pressurized air in front of it. This pressurized air can actually stop the water from flowing, especially if debris gets into the hose and blocks or partially blocks the inlet in the sink drain. The air gap provides a way for the air to escape, so this doesn’t happen.

The air gap’s placement on the sink deck or the countertop requires one hose to rise from the dishwasher to the underside of the countertop and another hose to fall back to the drain, forming a loop. The dishwasher pump provides enough force to get the water to the top of the loop, and from there, the water gets help from gravity to flow to the drain.

The air gap also protects the dishwasher from contamination from a drain clog. When water flows backwards from the drain to the dishwasher, it spills out of the air gap rather than going back to the dishwasher. Atkinson explains: “If your sink drain gets clogged and water tries to back up, it will simply flow out of the air gap and onto the countertop (a bad sign for sure), but it will not flow into the dishwasher hose. Kind of like a fail-safe.”

Do I Need an Air Gap?

It depends on where you live, as home repair expert Kevin Crawford explains: “Not all states make air gaps mandatory. Some areas allow what’s called a ‘high loop’ instead. That’s when the dishwasher drain hose is mounted up as high as possible under the sink, usually secured to the underside of the countertop, before it loops back down to the drain. It’s better than nothing, but it’s not as good as an air gap.”

According to Atkinson, states that require air gaps are generally those that follow the Universal Plumbing Code (UPC), including California, Washington, Hawaii and Minnesota. States that follow the International Plumbing Code (IPC), such as Florida and New York, are more likely to permit the high loop. “That said,” continues Atkinson, “some local codes absolutely require a proper air gap. So if you’re remodeling or installing a new dishwasher, it’s always smart to check your local plumbing codes or call out a plumber.”

About the Experts

• Kevin Crawford has over 20 years of experience in luxury real estate. He is the co-owner of TexFix, a company that provides home repairs and improvements in the areas surrounding San Antonio, TX.
• Alex Atkinson is a plumber and HVAC technician at Super Brothers, a Northern California-based plumbing and HVAC repair service.