Drinking straight from crystalline mountain streams is nice in principle, but a lot less awesome when you end up running for the bushes every five minutes for the rest of the trip. There are plenty of ways to help save yourself from waterborne bummers, but none that are as effective, easy to use, and reliable as the Guardian Purifier System from MSR. Developed for, and in conjunction with, the US military, the Guardian uses new Hollow Fiber technology to filter out just about everything protozoa, bacteria, particulate, and even viruses, so you can sip fresh, clean water without first checking that you packed extra TP. The Guardian has an easy pump action design that can filter up to 2. 5L per minute, and an ingenious self cleaning design 10% of the water from every stroke flushes contaminants from the filter, so it never gets clogged or becomes less effective. The wastewater is discharged through a tube that runs parallel to the intake, so it empties easily back into the water source. MSR also included a water bottle adapter for easy fill ups, and a cartridge life indicator that lets you know when it's time to switch although the included filter is good for at least 10,000L, so it might be a while before it's that time.