Board Thread:Theories and Speculation/@comment-35850816-20180611181629/@comment-25122992-20180613164129

Creating water from your own chakra (i.e. spilling it from your mouth) isn't quite the same as creating it from the air as Tobirama did. It's an exteremely difficult feat to do such a thing without any water source, while water creation from the user's chakra becomes a source of sorts. Thanks to the enormous chakra reserves, Kisame could spam this chakra-water convertion as he saw fit, while Tobirama didn't need this or a pre-existing water source in the surroundings at all.