I'm similary to claire, before exante my regular intake was at least 3 litres of water a day, (but I don't drink much else, can't stand tea/ coffee etc). I've increased it a bit so probably now drink 4-5 through the day. But you need to be careful, if you take too much water that's not good for you and can give you headaches, and worse. Just drink little and often and you'll be fine. I would aim, as the others have said for the 2-4 litres through the day, and see how you get on.