If you would have water in the tub, and you left the handheld shower submerged in the water - and if there was a vacuum in your water line - it could suck bath water into your potable water system.

The vacuum breaker will allow air into the system - thus there is no chance of contaminating your drinking water. Dish washers also have vacuum breaks.

You can get vacuum breaks that are part of the elbow connecting to the shower arm.

It's a highly unlikely scenario.

No peeing in the tub. Got it. LOL.

It helps to know the purpose of the item in the world of building code, but guess I can't guarantee perfect use and therefore we should install this if possible. Thanks.

So behind the wall, it would be one pipe that mixes hot and cold running up from the valve, vacuum breaker, shower nub going through the wallto out in front of the tile, then the 'supply elbow', then shower hose?

This post was edited by kats737 on Thu, Nov 6, 14 at 15:24

You don't have to open up the wall. Just Google handheld shower vacuum break. There are several types

Here is a link that might be useful: Hand held vacuum break

Gotcha thanks. I feel much better about being able to put this in, then. The picture of the item in use in that amazon link is super helpful - seems like it will go inline with the hose without too much headache.