Paying for water is not a new concept. Bottled water is sold in stores, vending machines, service stations etc everywhere. It's like buying any other good- you can either pay for it or not have it and find an alternative such as bringing your own.
Edit:
In an e-mail to The Huffington Post, an airline spokeswoman said Roslin "was causing a disturbance and attempted to incite other passengers to the point that another passenger started to cry in fear as a result of his behavior."
I could probably imagine what happened. Said surgeon requests water but either does not have enough money or does not want to spend money to buy it. Rather than being more prepared next time he tries to spark protest and outrage among the cabin and is subsequently removed. If anything the lawsuit should go the other way.
Just because water is generally freely available does not mean that it is not a good. Likewise, things such as sand are frequently sold in bags despite being freely available on the beach. It doesn't mean you have to go into a hissy fit if you for some reason cannot buy it.