The reason to use distilled water is that is is a contant. The suff from the super market is pretty cheap and it will always be the same clear clean water. Depending on where your tap water comes from it might have a lot of minerals in it. Why recomend using tap water for someone who wants to know what to use when I have no idea of the quality of their water supply. Thus distilled water.
If you are switching between a track mix and the usual 50/50 street mix as necessary you will never get it all out of the system and surely leave enough AF in the system to lube the waterpump.
As far as how fast AF/water mix evaporates, you may be correct, but the group(s) I run track days with ask nicely that everyone NOT use ANY AF on track for the simple reason that if they didn't someone will surely fill their car up with 100% AF and then blow it all over the track. Therefor I abide with the rules because I tend to do so when asked nicely and for good reason.
Ron your surely correct, there is a lot of wifes tales on a lot of stuff like, oil quality, air instead of nitrogen in tires, water or AF in coolent systems , and on and on. The cool thing is this forum gives everyone a chance to make their case on a subject and present what from time to time is some really good information.
At the end of the day, a forum member can usually count on soild, informed, usable information here. Thanks for that.