Every year my rental house is inspected by the city. Last time the inspector told me to add a backflow preventer (one-way check valve) to the handheld showerhead in the bathroom. The showerhead is on a long enough hose that it could be submerged underwater in the bathtub, and this would prevent drawing tubwater back into the water supply. (That bit seems a little hypothetical to me, but no matter.)

My problem is I can't figure out where to get one. The home centers only have garden hose backflow preventers, and nobody there has heard of one for a showerhead. I suppose I could call a plumber, but that would cost me a housecall, and I'd rather just install it myself.


They're also known as vacuum breakers, such as this one. Some searching shows that they're available from Lowe's and HD (assuming you're in the US), but you should be able to find one in a store near you or online if not.

  • You learn something new everyday... I've never heard of (or seen) a back-flow preventer on a shower head. Is it possible these are built into most handheld sprayers? – Tester101 Jun 9 '11 at 21:00
  • At both Lowe's and Home Depot, they told me they don't have them. But a search on "vacuum breaker" shows Lowe's does. So I ordered one from the Signature Hardware site. Many thanks! – Carl Raymond Jun 9 '11 at 21:04
  • @Tester101 - to answer your question, yes, vacuum breakers are built into the hoses of most handheld shower sprayer kits, normally on the end where the hose connects to the diverter behind the overhead shower head. – KeithS Jun 22 '11 at 19:01

The backflow preventer valve is usually built into the shower hose itself. Check inside the supply end of the hose. It's plastic with rectangular holes around the sides.


Sorry to disagree with Niall, but I've never heard of a check valve being referred to as a vacuum breaker. A vacuum breaker could be used for this purpose, but the efficacy would be questionable since, even in the best-case scenario, it would not prevent backflow of the water in between the vacuum breaker and the tee from which the hose is fed, and I don't think the inspector would approve it. Attempting to pass it off as a check valve might even annoy the inspector, and pissing inspectors off is a really bad idea because they will then go over everything with a fine-toothed comb and throw the book at you.

If your water pressure is low or just right, I'd go for the swing-type check valve. These feature a door that is pushed completely out of the way of flowing water, but if water flows in the wrong direction, gravity and the water flow will quickly snap the door shut. (Diagram) Since gravity is crucial to the operation of a swing-type check valve, the orientation of the valve is important. If it is mounted in a horizontal orientation, the hinge of the door must be on top. If it is mounted in a vertical orientation, the intended direction of water flow must be upward. This causes gravity to help shut the door, and it also prevents scenarios where the backflow is very slow, failing to create enough force to overcome the gravity pulling the door open.

If your water pressure is too high, use a spring-type check valve, which features a spring that pushes a ball, forming a seal if there is no water pressure forcing the spring to compress. (Diagram -- water can go up in this diagram, compressing the spring, but if it tries to go down, the ball forms a seal) Since the ball and spring never move out of the way of the water flow, these types of check valves slow the flow of water down.

Almost every hardware/HI store that carries plumbing hardware will have check valves. Both Lowes and HD carry them in multiple sizes and materials, but I don't think Lowes carries the swing-type check valves.

As Smapa has said, it is possible that a check valve already exists in the hose. Look for a bulge in the line that looks something like these pictures (1, 2, 3). If you see something like that, remove the hose and try to blow air in the direction opposite of normal water flow (keep in mind those bits about the orientation for swing-type check valves.) If you can't blow air through, there's a check valve in the hose. Call the inspector and ask if he will approve this if you can demonstrate that it works. If he comes over, be sure to know how to reattach the hose. If it is a gasket connection, you just have to tighten it down (but not too tight, as overtightening can tear the gasket.) If it is threaded, you need PTFE tape (watch a youtube video to learn how to use it) or pipe dope. Don't look like an idiot putting it back together wrong in front of the inspector; see last sentence of the first paragraph.


Backflow preventor is in the shower head. If you take shower head off and look at where it screws on to pipe you will see a little green piece under the rubber washer. They come with shower heads now and a lot of people take out because it also can restrict flow or if head is old enough would not have come with one in it. I guess now local plumbing code requires this especially if in a tub. My head is by Moen and it has right in instructions to install with back flow preventor as required by local plumbing code. Hope this helps

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