I have to admit, I have never water fasted on distilled water!
Tried it -- and couldn't stand it. Maybe if I'd had a home distiller, and could add back in a few (only a few) grains of Himalayan salt, just to lend it some trace minerals . . . To me, distilled water never has tasted wet, and always has felt like liquid plastic--but of course that's the only kind I've tried; what they sell in plastic bottles in drugstores.
When I've tasted rain sometimes, long ago, that's a whole other thing. But these days, I would not drink the rain. :-)
I'm pretty sure the plastic-y stuff is not the kind of distilled water the "fasting masters" had in the old fasting clinics. When I did my Water Fasts (check my old posts if you are interested) I always drank the water I usually drink, which is a spring water that's delivered. In the ceramic crock that seats the bottle is some very old "Prill beads" that have been there for years, supposed to make water wetter, and this water has always tasted/felt very good to me.
Even with that said, I almost always have only wanted to sip it boiled, and hot or almost hot, on a water fast, esp. on the longer ones. (29, 21 days) There is no way I could drink the tap water around here, although I too have widely read that bottled is the same as tap.
A water jug with a filter, like a Britta--I agree with Archus, that makes pretty good water, and i used one for a long time before getting spring water.
I would not use Dasani (believe it really IS like tap water),
or SmartWater--which simply has too much going on to be good for a water-only fast--it is more suited to people eating, or perhaps intermittently fasting (one day on, one off).
One more thing you can do with water on a waterfast: put water in a dark blue glass, or in a dark blue bottle. Do not cover with a metal lid, cover with a dish, an upside-down glass or a tissue... Only an hour in the sun is enough, and the water is good for clearing memory. We are mostly made up of water: Water has a long memory, and holds vibrations.
The blue solarized water helps the body to let go of the past. I've been told that all healing is release from the past, and have found that to be a profound truth that keeps on revealing itself.
The solarized blue water has a way of 'cleaning memory'. (It's used quite a bit in "Ho'oponopono", also)
beyond all that, it simply makes a nice change, on a water fast.
:-) I've thought of using other colours also, violet really appeals to me--one of those Miron glass bottles.