We were in a large CG with a few hundred feet elevation difference from upper to lower sites. Someone at the bottom left their site and forgot to remove their city water hose. It ripped the faucet off and the CG had to shut their main supply valve off. So that set up the scenario for water being drained by gravity from all sites above the damaged faucet into the water distribution PLUS water from lower sites being siphoned back into the system. And if someone were flushing their tank and had no backflow prevention, could have contaminated the entire CG. We were leaving the CG that morning and didn't have to worry.
There are many, many real life scenarios where backflow and contamination can occur. It's not a theoretical other universe possibility. Go talk to your local public health authority and see what they say instead of being ignorant and possibly making others sick (or worse).
