Submitted by Eric Daniel
No one these days thinks much about potable water in the field. When I was in Iraq in 04-05 we had a blivet farm on-site with 250,000 gallons of fresh water on hand, not to mention pallets of bottled water every 100 feet.
Back in the "old" days though, drinking water was not a sure thing. During the '91 Gulf War, before the shooting started, our fresh water came in the form of a hyper chlorinated 400 gallon water buffalo delivered every week. There was so much chlorine in the tank that you couldn't consume the water until seven days past the fill date, to give the chemical a chance to evaporate. Some days we'd get an early "drop" and have to stare at the buffalo for a couple of days while we waited for the born on date to expire before we could drink it (though before that time it was great as wash water.) Once the shooting started though, you were down to drinking out of your jerry cans.
Those days, however, are long gone. Nowadays, folk drink their water out of a bottle, and before every mission they'll toss a couple cases of the "good" stuff in their vehicle and head outside the wire (by the way, if your unit is one of those who opts for the 5-gallon jerry cans filled with bulk water, that's great, and I'm not bagging on those units that did that. All I'm saying is the units I worked with didn't do it.)
Unfortunately, I think this is a bad practice to get into. As soldiers, we can't always rely on mountains of bottled water everywhere to meet our needs. There may come a time when you're going to be out and about and you're going to have to make your own water, the old fashioned way.
To this end, I have taken to packing a portable water filtering pump. My choice is the MSR Miniworks EX water filter. Hand operated, the EX will filter 1 liter/min, and with a combination of charcoal/ceramic filter element, the EX can be cleaned and maintained for years of field service (there are no accessory parts to pack and it does not require tools for field stripping.)
The EX filter will strip out anything larger than .2 microns, which accounts for most bugs like crypto and giardia, as well as particulates (sand, rocks, etc...)
A word of caution though, the EX IS NOT a purification system. It will not kill viruses, and it will not sterilize the water. If you're going to use the EX to filter drinking water, I'd also suggest you use a secondary means of actual purification, such as boiling or iodine (or their equivalent) pills.
Despite this limitation I still prefer the EX over total purification systems. Purifiers typically require the addition of a chemical agent to purify the water, and are not designed to operate without it, so if you lose (or run out of) the chemical, the purifier becomes dead weight. At 16 oz. the EX is also fairly light and easily packed.