I was also going to ask about showers ... most natural consequence IMO is showers (the next day, or 3 days, or week - whatever would be appropriate in your eyes) and then bath privileges resumes ...

I also wonder whether it's better to make it about your DS ("now that Penguin is here, we need to be careful about things which could be dangerous for him - so if you want a bath, you need to stay in the bathroom while the water drains completely") or whether you think you should distance it from him, so it's not perceived as being an inconvenience which is his "fault" ("you're 9, you're plenty old enough to bathe yourself, and part of that is keeping your bathroom clean - including the bath ...")

Just a (tangential) thought