I only meant the coffee filter to get the chunks out. (g)
You can't do much better than rain water. NYC drinks rain water, from reservoirs upstate. Grand Rapids, MI pumps their drinking water out of Lake Michigan. In both cases, it is what they do afterwards to it that makes it unpalatable.
Since the OP was interested in survival, I would expect that, if in that situation, he'd probably be quite pleased with rain water. I'd sure want a gulp of something while rigging up my saltwater enema.(G)
I am a water well driller and I always chuckle when people, usually women, see me drinking water being pumped directly from their well. They, with a superior tone of voice, announce that they only drink bottled water. I've given up on trying to explain where that comes from.
“Scientists are people who build the Brooklyn Bridge and then buy it.”
Wm. F. Buckley, Jr.