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Why Do I Need A Vacuum Breaker?

By In TISH Repairs, Truth-in-Housing, Vacuum Breaker On January 17, 2009

Vacuum Breaker

Vacuum Breaker

This is one of the most common questions I get from homeowners that I do Truth-in-Housing Evaluations for.  If you’re selling your home in Minneapolis or Bloomington, you will likely hear about this.  A vacuum breaker, commonly referred to as a backflow preventer, is a device that prevents the potable water in your home, and possibly even your neighborhood, from getting contaminated.

How could your water get contaminated? Picture this scenario: I want to mix up some vegetation killer, so I buy the concentrated stuff, pour it into a bucket, then put the garden hose in the bucket to fill it.  I turn the water on, but I get sidetracked with a plumbing project.  I shut off the water to my house, and then open up the laundry faucet to drain the water out of the pipes.  This will create a siphoning effect, which could actually suck the nasty chemicals in the garden sprayer back in to my home, contaminating the potable water.  An even worse scenario would be the city doing work on the water pipes, and the chemical gets siphoned back in to the city’s water supply, contaminating a whole neighborhood.

While these occurrences are not likely, it has happened many times throughout the country, and the cost to fix a contaminated water supply for a city is huge. The cost of a vacuum breaker is very small – about five dollars.  While only Minneapolis and Bloomington enforce vacuum breakers, they’re still required throughout Minnesota by the Minnesota State Plumbing Code, section 4715.2100 (D).

The two most common places where these are installed are at sillcocks (what you connect your garden hose to) and at laundry sink faucets.  An external vacuum breaker is required at sillcocks if they don’t already have one built in.  How do you know the difference?  The photos below show one sillcock with, and one without an integral vacuum breaker.  If a sillcock doesn’t have the little mushroom cap, an external vacuum breaker is required.  At laundry sink faucets, a vacuum breaker is needed if there are threads present that a garden hose could attach to.

Standard Sillcock

Sillcock with integral vacuum breaker

For more information on common Truth In Sale of Housing defects, click on any of the links below.

Reuben Saltzman, Structure Tech Home Inspections – Email – Minnesota Home Inspections


About the Author


Reuben is a second generation home inspector with a passion for his work. He grew up remodeling homes and learning about carpentry since he was old enough to hold a hammer. Reuben has worked for Structure Tech since it was purchased by Neil in 1997, and is now co-owner and President of the company.


  • lisa 7 YEARS AGO

    Thank you for explaining why the city of warren,MI has a requirement for installing vacuum breakers on sillcocks and laundry tubs. I believe it would require a completely stupid, thoughtless person to actually contaminate their potable water the way you've described it (something I'm willing to bet one of the five totally incompetent building inspectors has managed to do) but as improbable as the set of circumstances are that would lead to this you've made it make sense to someone with a good understanding of plumbing systems who keept wondering why you would need a vacuum breaker attached to something that closes completely with a valve and has water pressure pushing against it.

  • Reuben Saltzman 8 YEARS AGO


  • Paul Sorensen 8 YEARS AGO

    Thanks for the great info. I found your site while trying to figure out what that brass thingy was on our outdoor faucet. Your explanation is fantastic.

  • Craigslist verified accounts 8 YEARS AGO

    I'm don't comment often, but I do like your blog