Sex is not compatible with a water fast. (the chances are, you won't want to entertain the notion, once it really begins--anyway, it would be a misuse and misdirection of the body's vital energy. If you are thinking that one week off this product might make you fertile AFTER the fast, I don't know bout that...I didn't know neem was an effective form of birth control.
at any rate--you do know the answer to your question. "water fast", unless you are doing something else entirely, which would be like starving yourself, and giving your body herbs at the same time. It will not go into fasting mode: autolysis etc.