Okay my exercise says the following: "By applying a pressure of 200 atm, you can compress water to 99% of its usual volume. Find the work needed to do this." Now I'm having a bit of trouble with how this is put. For me it doesn't make sense to just put 200atm pressure on normal pressured water vapour. Don't they mean between the lines, that the water has been slowly pressured quasistatically from normal pressure to 200atm pressure?