[@rivaan]
Sorry, you can't just pull water out of the air unless it's say a sauna or raining. Also, while it is possible to draw from plants just remember that culturally doing so is seen as a bit 'dark' as water benders tend to promote life. He can have whatever opinion he wants on it, but overall it's how society views it. Also, he can not be a master just upon learning it in his history. It's a martial art in the world, without knowing the movements he couldn't be a master at bending right away from being self taught as seen with Katara who was a prodigy herself as revealed by how fast she learned at the North Pole, but never a master until after she got their and had combat experiance. He can be naturally gifted however like Aang and Korra having learned fast to become a very skilled bender to the point of being a master by the end of his training.

Also, I'm sure even the Dark Avatar kept this law, Blood Bending is HIGHLY illegal. Even being suspected as one can land you in jail as well as being completely morally wrong in the world. Just making sure you know!