Being an ex-Army Combat Medic, I tend to be much more meticulous than most about filtering and purifying my water while on the trail. In fact, I usually filter and purify the water I plan to use with either mixed-oxidants (MIOX) and/or with UV light (SteriPEN). Both methods are extremely thorough when used properly, and generally only one method is necessary.

The MSR^® MIOX^® and the SteriPEN^® are equally well designed, yet each takes an entirely different approach to water purification.

It is important at this time to understand the difference between "filtration" and "purification". Filtration implies straining the water through a physical filter, usually paper, fiber, or ceramic. This method is designed to remove particulates such as silt, dirt, other solids, and larger bacteria from water, but does not actually kill any bacteria and/or viruses found within it. This step makes the water look clearer and can make the water taste better.

Purification by itself does not remove any particulates, as the water is not passed through a filter. Purification utilizes chemicals (such as chlorine or mixed-oxidants) or ultraviolet light to neutralize viruses and bacteria. This step makes the water safe to drink.

In order to make water absolutely safe and pleasant to drink, suspect water should be both filtered AND purified.

Filtration is pretty straightforward, and the method used generally falls to personal preference. While ceramic filters may tend to be slower, they are usually easier to service in the field and can capture more particulates than a paper filter. However, ceramic filters are generally more expensive than paper filters and can weigh many times more than a paper or fiber filter. Paper and fiber filters are light and very easy to use, making them a common choice for backpackers. Ceramic filters are usually harder to pump water through, also, making them slower and more tiresome.

For comparison, a hollow-fiber filter such as the MSR Hyperflow filtration kit can filter water at up to 2.75 liters per minute, ceramic filters at up to only 1 liter per minute, and the paper-cartridge filter at up to around 1.25 liters per minute. The advantage of MSR's hollow-fiber filtration system is obvious, as it clearly out performs the other options in both flow rate and size/weight categories.

In most situations, however, filtering your water is only half the battle. Your water is now visually clean, but requires purification before it is completely safe to drink. And, unlike filtration, purification usually involves more than a little guess-work as most methods do not provide feedback in any form to indicate whether or not this process was successful, and drinking contaminated water can have deadly effects.

For many years, for example, the U.S. Military used iodine in both tablet and liquid forms to purify drinking water for our troops in the field, and then used chlorine in more recent years. The person treating the water had to first estimate the quantity and then the quality of the water, and add the amount of purifier that they deemed to be an appropriate amount of purification agent based on these results. In most cases, this involved "over-dosing" the water simply for safety's sake. Unfortunately, this method almost always resulted in foul-tasting water.

On the trail, knowing the quantity of water is relatively easy, as most of us use containers of a predetermined size, such as a 1-liter Nalgene bottle or 3-liter Camel-Bak bladders. It is still necessary to ascertain the quality of the water we intend to treat, however, and guessing incorrectly could go so far as to result in death if conditions were to be grossly underestimated.

The inexpensive (and often preferred) method of purification on the trail generally relies on the "tried-and-true" method of iodine or chlorine tablets, but still requires a great deal of luck.

The newer and safer methods available leave far less to chance, create safer, better-tasting water, and can even offer verification that the water is indeed safe to use.

The easiest method I will discuss uses ultraviolet light in both the UV-A and UV-B range to effectively kill all bacteria and viruses hiding in your water. This method is highly cost-effective and fast, making completely safe drinking water virtually "on the fly". The Steri-Pen is very small; roughly the size of a small AA-battery flashlight. One particular model uses rechargeable CR123A batteries which can be charged on the trail using an optional solar charger, creating a great long-term solution to water treatment either in the field or during an emergency. Although this method works almost instantly when used per the instructions, there is no way provided with the device to test the treated water to make sure it is safe to drink.

Another field-expedient method allows you to create your own mixed-oxidants (MIOX) on an as-needed basis. Not only is this product extremely easy to use (just add water and salt, shake, and press a button), it also offers positive feedback pertaining to the quantity of mixed-oxidants in your treated water, giving the user a fairly accurate view as to the finished quality of the purified water. It is important to note that with this method, it may take from 15 minutes to 4 hours to create water safe enough to drink. Test strips are included to indicate the amount of mixed-oxidants present in the finished water - invaluable feedback for the user.

When the quality of the water being treated is unknown - as is usually the case - over-dosing the water is highly recommended. Double or even triple-treating the water is sure to provide water that you don't need to be worried about. Carefully filter the water through a reliable pump such as the MSR hollow-fiber HyperFlow filtration system and then purify the water to three times the quantity than you actually need (i.e. treat 1 liter as 3 liters), assuring that you have safe drinking water as you need it. Better yet, purify your water using (u)both(/u) of the methods listed above (UV and MIOX) so that there is little chance of drinking contaminated water.

Remember, clean-looking water does not mean safe water!! In fact, dirty, purified water is usually safer to drink than filtered non-purified water!