Quote:
Originally Posted by jempat56
I’m not sure I understand your explanation. How can a pressure drop create a backflow unless the valve is actually open. Even then how much “contaminated” water is in the hose? I’ve never seen these backflow preventers anywhere till I got to the villages. Is this a local problem or just a fix for a non existent issue. Interested to hear your thoughts.
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It is not a local problem. Potable water systems are always designed to prevent backflow and not just from the outside hose bibbs. If you notice, all of your sinks and tubs inside the house are designed so that the faucet discharge level is always higher than the overflow level of the sink or tub and they do not have a threaded hose connection. So, if the sink or tub overflows, the water cannot backflow into the faucet. The outside hose bibb is designed to have a threaded hose connection, and the concern is that the water in the hose can have bacteria in it, or someone could insert the end of the hose into a bucket containing harmful chemicals. Then, if there is a water leak inside the house or in the water main, when the hose bibb valve is open, a negative pressure can suck the contaminated water into the house piping. That is the reasoning for requiring a vacuum breaker on the outside hose bibbs. Basically, it is a universal plumbing code requirement.