agree with Kate here, on the likely part that fear has played for you. Shelton writes about "nerves", (no small potatos, if you suffer them). Purinton's fasting manual is great for cutting though conventional thinking about water fasting, ans showing you where you might have fears that need untangling.
That you say you hadn't heard about the preference for distilled water says you've only been reading bits and pieces. It's SO SO important to prepare yourself, mentally by studying some of this fasting lit. until you are somewhat saturated with it. Then you will know also, to drink only according to thirst. And that boiled, hot water can help soothe intestinal 'collywobbles'. Tap water is just plain not good. Should not be drunk. At least, filter it. But I do not think spring water is so bad. I did all my fasts with it.
EFT can soothe fears and all sort of ups and downs. If people only knew how 'magic' it can be, everyone would learn it--a child could pick it up in five minutes or so.
Some people would do well to have some Bach flower essence like Rescue Remedy or Mimulus at hand, if they tend to be anxious types. The RR is something to take instead of/before going to the ER. You can take it on your wrist, or your crown, or put a few drops in the bath.
Reading the fasting lit too would acquaint you with the knowledge that you will revisit former complaints, on the wfast, and once you see these through, they will be cured.
it's about 'no fear'.
sending you some of that, may you be well,
form now on