Well I have always weighed in first thing in the morning before any water or shakes in roughly the same clothes everytime. As long as you weigh at the same time every week you should still see the weight coming off. Don't cut back on the water coz they say, the more you drink the more you shrink, and it would be dangerous to try and get too much water into you afterwards if you do it too quickly as you could overload the kidneys. If I were you, I'd have a shake and plenty of water in the morning (and lots of wees!!!) then just sip water from about 1pm when you are thirsty until WI (make sure you have a last wee!!!!) then have your second shake afterwards. This may not work for you but you'll soon find what does. Whatever you do, do roughly the same each week so you can see your progress.
Good luck.
x