I always thought that Penelope putting hair ties in her water bowl was a way of telling me to step it up and get her some clean water.
Apparently indoor cats put toys in their water/food bowls because they see it as a safe and secure place, as “their” place, so other cats? can’t get their stuff.
Which is dumb, because I’m the only other thing in this house and I always find them. Try putting them behind the washing machine or under the bed.
Learn som'n new every day.