HCA: Hermit Crab Association

for boiling would it be okay to boil in tap water, or salt water make from table salt.... just for boiling, not drinking/bathing!

Perhaps. Like you want to blanch a clam or a few shrimp to feed, that should be fine, I suppose. Usually I boil with the water that I use for my own food: ex. water filtered by a Brita brand filter.

It probably would not do too much harm, although, if you have dechlorinator on hand, it doesn't hurt to add a few sprinkles.