Some older homes & buildings have this problem in Australia. It might be worth letting guests know in the house manual or a little note in the bathroom that this can occur, as not everyone could be expected to know this. On the other hand, it could also be a great way to get guests out of the shower when they've been in there too long - just leave the tap running in the kitchen 😉
I'm in a new apartment building, but we have rainwater tanks for the toilets. Sometimes the water in the toilet can be discoloured, so I have a handwritten note above the toilet to let guests know this so they don't freak out! And I also have a reminder for the ladies and some paper bags in bathroom cabinet so they don't flush sanitary items down the toilet and clog it...