That sounds fine to me and what the Cambridge diet recommends. Lighterlife people are encouraged to drink 7 pints (4 litres). Though the general opinion is the more you drink, the more you shrink...it never worked for me and I felt baaaddd on more.
As for your original question. Yes, if you are adding extra to your shakes, you can deduct that from the 4 pints. Only the extra water though.
Hope that helps
