As far as I do know, most people here have fasted entirely without supervision, except perhaps someone to check in with.
It'a a rare luxury for many people to think of a fasting clinic...but sometimes. for some, it's a lifesaver.
I should add---I believe the ones who've had the easiest/best time of it, (all that being relative), usually made use of the huge resources out there-- that are always talked about, here,
Soil and health library--online books on water fasting...
Natural Hygienic Society (lots of links)
If you can afford and feel that a supervised retreat is the right thing for you, then -- all the best!
Just know that although no one should encourage you to do so, many HAVE water fasted without such support. And been fine.