If you don't see it in supermarkets, try an auto supply store! You're supposed to use distilled water in your car, so you might find it there.
There's a slim chance that your tap water is pure enough. Boil a gallon down to the bottom, if you don't see anything while or crunchy then you're good to go (unlikely)
You can buy distillation units but they're expensive. If you make your own, you have to boil water, collect the steam rising from it, condense it with cold and there ya go. I think the cheapest and easiest way would be to collect condensation. Dig a hole outside, place plastic tarp over hole with small hole cut in plastic, weigh it down so the water will to the center and down plastic hole, into a cup you've placed there.
Nah, just go find some jugs at the store [img]http://www.**********.com/iBhtml/non-cgi/emoticons/wink.gif[/img]