Rthur's absolutely right in talking about salt regarding the cleaning of CI. I can't say anything to the aluminum foil, though I'm not arguing at all. I've just never done it. My main point of what I was saying, for clarification, when I said "only water" was that NO SOAP be involved.
Some even use gravel/sand in the stream-bed when camping, to clean. Sure, fine, and dandy. Just don't use soap and you'll continue to be happy. And the more you use the pan, the more it gets seasoned, and the more the pan gets seasoned, the more you'll want to use the pan. Just think of building an 'eggshell like covering' one micro-layer at a time. The thicker it gets, the gooder it is.
The less you abrade or etch said covering, the better. Acidic foods such as tomatoes and whatnot, can 'etch' the surface. Take that into account, also.
But don't be afraid of CI. It is the premium cookware, and only adds to your talents. Aluminum pans covered with teflon are the Super-Sniper Scopes of the kitchen. Keep that with your pantry full of Kraft Dinner boxes, Itchy-bum noodles, and other pre-packaged foods.
Cast Iron is for people who COOK.