Dishwasher Backflow Prevention

Many people do not realize that installed appliances such as dishwashers are a part of the standard home inspections performed by Blue Star Real Estate Inspection Services.  A common deficiency which I see in dishwashers is the lack of a proper air gap.  An air gap is a means to prevent dirty water from the dishwasher drain from contaminating your water supply system.  There are two ways to provide a proper air gap for your dishwasher.  One way is to install an air gap device similar to the one pictured below.  This is simply a device which provides an air gap in the drain above the rim of the sink, effectively preventing backflow into the dishwasher.

air gap device

The picture above diagrams an air gap device for a dishwasher.

Another acceptable air gap method to prevent backflow of contaminated water is to simply route the drain hose in a “high loop” that is secured to the underside of the countertop, higher than the sink level.  This method effectively forms an air gap in the drain hose which prevents drain water from being siphoned into the dishwasher.


The illustration above shows the “high loop” method of backflow prevention which is commonly seen during inspections.


The photo above shows a dishwasher drain that does not have a proper “high loop.”  The drain hose should be secured to the underside of the counter.

Nowadays most, if not all, new dishwashers come with a loop built in to the drain hose.  This is NOT a substitute for installing anti-siphoning devices as listed in this post.  You should always have a visible means of backflow prevention installed on your dishwasher.dishwasher high loop

High loop shown in a new dishwasher.  This alone is not acceptable as a means of backflow prevention.

An air gap is the only method of backflow prevention for dishwashers that is guaranteed to work in all circumstances if installed correctly.  When your home is inspected by Blue Star Real Estate Inspection Services, we will ensure that the proper measures have been taken to prevent backflow of sewage into your dishwasher.

Call 361-462-9018 to schedule your inspection today.


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