This can also mean "He (she/it) can fill the bath with water." Aqua can be nominative or ablative. Unless there are macrons over vowels, you can only tell which of the two cases it is from context.
Balneum refers to the room itself, not to the tub, basin or pool.
It sounds to me as though the final -t of potest was inadvertently cut off. (I heard potes , you can.)
ego quoque. duo accepted potes as a typo.
That's what I heard, too. I thought 'Aqua' was ablative.
Why doesn't it accept 'the water' instead of 'water'?
It does now.