Jadnashua
Retired Defense Industry Engineer xxx
You at the minimum want a vacuum breaker, either built-in, or add-on. In many places, a backflow preventer is required, and in many places, it must also be tested by a certified tech as often as annually to ensure it is protecting the water supply. Yes, it takes a special set of circumstances to happen, but you can contaminate your home's water supply. One possible scenario is if there's a fire nearby and they are using all of the fire hydrants to maximum flow while your sprinklers are on. You could suck up stuff into the supply lines. It could be something that you do, but more often something that happens in the system. A certified backflow preventer is moderately expensive, but the price many people pay to protect their and their neighbors' water supply.