Good luck with the fasting! It is a tough thing to do and one that was enlightening for me. I have done several water fasts but my longest were two 12 day stretches. I found it fascinating how much my head was involved in the eating and not my body!! My only tip for lasting the course has to do with the smells of food. I found that resisting them made my life harder. In the end the best thing for me was to go into the kitchen when the food was being prepared and chat and SMELL the food. Lean into the wind.
For the record though, IMHO if a cup of warm water with a tea bag shaken at it will help you through the day - then do it. It is a better alternative than giving up. I suspect that 40 days may become hard on your body - I think 30ish is probably quite sufficient. Truth to tell my body thought 12 was really quite enough thank you very much!
It is a magnificent feeling of achievement to do a water fast! Go for it!