Also, things like a water main break (someone screws up and hits it with the excavator) or a fire hydrant opened (to be flushed out, tested, or used for a fire) can also cause your hose to siphon back into your house and then to the main. You just have to read up on these situations to see how they can happen. Even if you are careful with your hose, what about your neighbor? Maybe he is not so careful.
I have read about cases where pesticides get siphoned back into the main from a hose bib that did not have a breaker. The question is that you don't really know how far is spreads or when the system is flushed "good enough" to drink when something like this happens.
This is why there are plumbing codes and is why plumbing should always be done with a permit and inspected. It is still not 100% foolproof, but it is sure better than someone who does not educate themself, does not get a permit, and thinks between the DIY book and the guy at HD that they can just figure out something that "works".
I have read about cases where pesticides get siphoned back into the main from a hose bib that did not have a breaker. The question is that you don't really know how far is spreads or when the system is flushed "good enough" to drink when something like this happens.
This is why there are plumbing codes and is why plumbing should always be done with a permit and inspected. It is still not 100% foolproof, but it is sure better than someone who does not educate themself, does not get a permit, and thinks between the DIY book and the guy at HD that they can just figure out something that "works".