On #2- figure out a test for your theory. One outcome means you are probably right, outcome two means there is probably another explanation. Run the test. Look at the results and don’t try to retrospectively change the answer- this is where people tend to go wrong. You don’t need more evidence, you need to move on.

…and a plan to do something about it right ? Which would be to do what OP originally suggested and shut off the water. You would need to monitor the feed and then get someone with access to your place to shut it off before everything is ruined, otherwise you have the same situation, but your holiday is also ruined through the knowledge that your belongings are being destroyed.