If you're selling your home in Minneapolis or Bloomington, you'll probably have to pick up a vacuum breaker or two. 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 in to 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, they do happen 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 as part of their point of sale inspection programs, they're still required throughout Minnesota by the Minnesota State Plumbing Code, section 4715.2100 (D).
Cheap vacuum breakers don't meet code, but...
Part of the requirement for a vacuum breaker says any new device must be field testable. The minimum standard for a vacuum breaker meeting this requirement is ASSE 1052. Vacuum breakers that conform to this standard are about twice the size of the really cheap vacuum breakers that you'll find at most home improvement stores, and they cost about four times as much.
Above left is a vacuum breaker conforming to ASSE 1052. You can see that it's about twice the size of the cheap vacuum breakers that conform to ASSE 1011, shown above right.
Cheap vacuum breakers are still allowed
So why do you see the cheap vacuum breakers all over the place in Minneapolis and Bloomington, and why are they allowed for Truth-In-Housing evaluations? Minneapolis and Bloomington allow these because they don't want to place too large of a burden on homeowners. They want homeowners to be able to pick up a cheap vacuum breaker at the neighborhood hardware store for a few bucks. I guess they figure it's better than nothing.
...but not on new construction
If you look at any new construction home or at any sillcock that has been recently installed with a plumbing permit, you'll find a proper external vacuum breaker or the sillcock will have an integral vacuum breaker. If the sillcock has an integral vacuum breaker, it doesn't need to be field testable.
The photo above left shows a standard sillcock with an integral vacuum breaker, and the photo at right shows a frost-free sillcock with an integral vacuum breaker. Both of these sillcocks meet the minimum requirements of the Minnesota State Plumbing Code.
Why Just Minneapolis and Bloomington?
So why is it that only Minneapolis and Bloomington require vacuum breakers for their Truth-In-Sale of Housing programs? I suspect there has been too much complaining from residents in other cities. Even though this is the cheapest, easiest 'repair' item required in Minneapolis and Bloomington, I hear more complaints about this one item than anything else.
The two most common places where these are installed are at sillcocks (what you connect your garden hose to) and at laundry sink faucets with threads that a garden hose could attach to.
ps - It's time to drain the water out of your outside sillcocks (faucets) if you haven't already done it this year. If you have a frost free sillcock, don't forget to disconnect your garden hose.