I Don't Swim In Your Toilet, So Please Don't Pee In My...Bathtub?

"He can pee standing up! He learned that a lot faster than I did. He's going to be ready to pee in a toilet soon." said Husband with excitement. Oh yes, came my reply - dripping with sarcasm, let's potty train our 9 month old! Obviously he is by no means ready to pee in a toilet. The reason for Husband's excitement is because EVERY time I put Grant in the bathtub in the past week he stood at the side of the tub and peed. Without fail every time. When I take off his diaper there is not the slightest indication that he has to go. Maybe it's the warm water? Who knows. But it makes him happy because he's grinning the whole time. Then he sits down and starts playing and I'm left standing there saying "Great, now you're playing in pee water." What to do? Change the water? I'm sure he's peed in the water before without my knowledge, yes? And it was only a little.