Hello anglynn,
dry fasting is essentially abstaining from anything except air and breathing.
Fonty may describe it as going for as long as is comfortable & safe without water, which can be anything up to 5 to 10 days or even longer I believe, but you will have to ask him that.
Dry fasting is essentially the same as Water Fasting according to thirst, as to deprive the body of much needed fluid is detrimental to health, after all it isn't wise to allow yourself to dehydrate. As long as the pre-fast diet contains predominantly high-water content food then there is very little demand for water on a fast anyway.