Is a 1 or 2 day water fast done during cleansing (using Garden of Life Perfect Cleanse) beneficial or harmful?

I'm currently using Garden of Life's Perfect Cleanse Kit. It's a 10 day program and I'm on day 7 but I haven't had very good results with it. I've been having headaches and haven't had a bm upon arising as it states I should be having during the program, so I'm wanting to accompany a day or two of the program by doing a water fast. The instructions state that I should drink plenty of water during the program and I am drinking lots of water already, but I am also eating normally throughout the day (my 3 meals, breakfast, lunch and dinner at regular times of the day - no junk food or fast food either). So do you think it would be safe or a good idea to do a 1 or 2 day water fast while I'm on this Perfect Cleanse program?