The Building Balloon, try "help Water", with a lower-case h. The help command is supposed to be lowercase (every built-in is) but ITR's prefers "Help". The newest version of the mod loader supports that as well, but that's not officially released yet.
I have to add everything that doesn't float manually, so it's only natural that there's some stuff I miss
Fireballs are supposed to float. Also, they don't actually burn, they just look like they do, like, if you try to ignite something with them, you won't succeed. If you start with the fireball underwater, the fire-effect doesn't start.
Same with torches, with the exception of the underwater thing.
I keep getting erros like this one (the water loads but i have no clue how to customize) and the "help water" command doesn't work) [Exception] NullReferenceException: Object reference not set to an instance of an object