Water purification

I think @Car Nut hit the nail on the head with a sledgehammer when he said 'Bottled Water'. I'm not much of an outdoors person. In fact, my idea of roughing it is a hotel room without a good mini bar, a good free breakfast and HBO. I would never voluntarily put myself in a position where I needed to purify my water.
That being said, when I went to USAF Survival Training, we spent three days and two nights in the wilderness north of Spokane Washinton. They taught us to use the tablets (iodine I think) after filtering it. They said to use a piece of any cloth available. They also said that boiling would work OK, but it was not as good as the iodine tablets.