It's really interesting to me that distilled water is what is recommended by gurus.
I've learned that distilled water is actually not healthy to drink over a long period of time. This is because of the absolute purity of the water, which changes the balance levels inside the tissues of the body and in doing so potentially damages cells.
Just food for thought.
I'd say this about what kind of water you should drink during a fast. People have been fasting for thousands upon thousands of years. Bottled/distilled/purified water is a relatively new thing in the history of mankind. Leads me to believe it's not imperative to fasting.