Water fasting.

Hello, I am new to Water Fasting but I have gained a quite a bit of weight over the last 7 months. I need to be back into shape by June 30,2012. I am planning on doing a 144 day fast starting tomorrow. Drinking just water and tea, and of course taking some multivitamins. How much weight would I lose? I am a female, 5'7 weighing 140-145. I am going to be very sedentary, moving as little as possible.