Dunno if this idea has come up already, but I found a nifty solution for a compact water storage container to use in small survival kits. Behold, the doggie poo bag! I've used these things a million times to clean up after my dogs and it just struck me that they would make a great water carrier. The photo shows a deployed bag on the right holding a quart of water -- with room for an additional quart. On the left is the same sort of bag folded up as small as a book of matches. One of these would easily fit in your wallet. Fill with water, tie the handles and you can carry this while hiking without spillage. Untie and you can pour out the water easily. They're cheap, available anyplace that sells pet supplies, and available in a variety of fun colors. Condoms are common in PSK kits because they are compact and durable. But if you've ever tried to use one for water storage, you know their limitations: Difficult to handle, hard to drink from and nearly impossible to reuse. These doggie doo-doo bags can be punctured. They're similar in strength to plastic grocery bags. So keep them off the ground and away from thorns and brush.