Why not just drink a quart of water once every 5 days? That'll give you plenty of dry fasting time without any (mostly irrational) fears of dehydration. I don't think you have to worry about dehydration as long as you're taking baths in unsalted (and perhaps unchlorinated) water. Hasn't it been reported that patients in some clinic in Russia do 30-day dry fasts?
I also recommend drinking spring water, which I personally find much more hydrating than processed waters. Fiji water is the best stuff I've tried. I don't know if it's just the silica (which you could add yourself to any water) or something else. I'm guessing the main thing that makes spring water superior is the natural structure (or energy, or vibrational frequency, etc.) of the water. I've dropped prill beads (inexpensive magnesium oxide rocks that are believed to restructure water) into some really flat, metallic, poorly-hydrating water (which I created using a low-quality $100 distiller), and in 24 hours the water tasted as fresh and vibrant as spring water. No exaggeration. I reproduced that result many times.