How long is it safe/healthy for a toddler to sit in the bath for?

[Flingmoo]

My toddler loves baths and on a rainy day he'll sit and play in the bath just as a fun way to pass the time.

The question is, how long is too long to sit in the bath for? Water not too hot and he's supervised at all times, of course!

Provided the temperature is okay, until he starts going wrinkly around the edges I guess.

Until the waters too cold(you can top up with warm) and when wrinkly they're done.

Just keep an eye out for dry skin as bathing is very drying