Bath Chair Puns

We're at a research conference this week, and my professor was the session chair. He started out with "we all know that H2O is water, but - and I want you to really think about this - what is H2O4?" He then shows a diagram of the molecule for us all to ponder. After a minute he says, "so, what is H2O4? For drinking, bathing, washing up..." Cue a room full of groans and chuckles.