MSR Guardian Water Purifier
Using .02 micron medical-grade hollow fibers, the MSR Guardian Water Purifier removes viruses, microbes, contaminants, and other particulates from even the nastiest of water. Its unique design automatically back-flushes 10% of its water with every pump, meaning you never have to manually scrub it, and it's also surprisingly durable, standing up to both freezing environments and drops of up to six feet. It can clean up to 2.5 L of water per minute, and since it's rated for over 10,000 liters before it needs a filter change, it might just be the last filter you ever buy.