How many ml of liquid per protein powder?

I think it's all to taste? I drown my whey in around 600ml? And then when I'm done, I fill it up again and swirl it around and make sure I got all the powder off the walls of the bottle and drink that 'dirty water'. But that's me.

Different protein types will react to water differently. I use minimal water in casein and make it into a "pudding".