Let's Talk About Water Purification
Water. One of the most important requirements when you are camping, hiking, or backpacking. Necessary for drinking, cooking, brushing your teeth... needless to say, you can't go without it. But unless you're lucky enough to be drinking from a pure mountain spring at 14,000' that's never been touched by another human, you probably want to treat your water so that you won't get sick. Let talk a little bit about the stuff you DON'T want in your water and your different options for treating it.
There are three main things that will make you regret drinking untreated water: cysts/protozoa, bacteria, and viruses. In the US, the cysts/protozoa are the baddies most likely to get you.
CYSTS/PROTOZOA: Giardia and Cryptosporidium will both give you some mighty big tummy troubles culminating in some epic diarrhea, so I suggest avoiding them at all costs. These guys are pretty big, however, ranging from one to 20 microns, so they get caught by filters. They are also easily killed by UV treatment. Chemical purification is acceptable, but not perfect (except Iodine, which is NOT effective against Cryptosporidium).
BACTERIA: Bacteria such as E. Coli and Salmonella are less common in the US in most water situations. This is because the USA has a pretty decent sanitation system and we don't dump raw sewage in our fresh water. Unless there is an animal carcass upstream of you or the water is REALLY nasty, bacteria usually aren't much of a concern. Some bacteria will get caught by filter media, but a few are small enough to slip through. Most are between .01 and ten microns. UV treatment and chemical purification will take care of bacteria.
VIRUSES: Also not as much of a concern in the USA. Viruses are species specific for the most part, so if a water source is infected with a virus, it's because humans have been behaving badly nearby, such as defecating too close to a lake or stream. The most common viruses are hepatitis, norovirus, and rotavirus. These guys are so small that they won't get caught by filter media - usually .004 to .03 microns. UV treatment and chemical purification will take care of viruses as well.
Now that we know a little about the things we want to avoid, let's talk a little about how to avoid them. The great thing these days is that there are many options that adventurers can use to protect themselves. Growing up, I only used a pump filter or iodine tablets. I don't know anyone who uses iodine tablets as anything other than a backup purification method anymore, and filtration has grown by leaps and bounds. In fact, I don't carry a pump filter anymore - now I use a Steripen, which uses UV light to purify water. My husband, though, still prefers his Katadyn filter, and my backpacking buddy loves her Sawyer squeeze filter. Let's break down our options by category.
NOTE: I ALWAYS recommend carrying a backup form of water purification. Whether it be Iodine or purification drops or tabs, or boiling, you need to cover your butt if something happens. Drops can spill, batteries can run out, and filters can clog. A tiny bottle of Iodine tabs weighs nothing and takes up no room. Throw it in your emergency supplies and don't worry about the expiration date, as these tabs last a long time.
FILTERS: There are three basic types of filters: pump, gravity, and in-line filters. The most popular is the pump filter, where you drop the intake line into your water source, work the pump to force water thought the filter media, and the clean water goes in your bottle or bladder. Gravity filters work the same way, except gravity is used to force the water through the filter media. In-line filters use the force of you squeezing the bag with the untreated water though the filter media, or the force of you sucking on the clean end of the filter to draw the water through the media.
UV TREATMENT: UV treatment works by using ultraviolet light to damage the DNA in protozoa, bacteria, and viruses, so that they can't infect or harm others. The go-to device on the market is the Steripen, which comes in several models. It requires batteries and treats up to one liter at a time. You need a hard bottle with this device, as the light needs to contact the water to work, so a soft water bladder makes this difficult and the results unpredictable. Your water also needs to be clear for this to work, so if water is silty or cloudy, it must be filtered though Steripen's pre-filter or a bandana. Make sure you pack extra batteries as well. These devices are great for travel in developing countries, where viruses are more of a concern because of inadequate sewage systems and hygiene practices.
PURIFICATION, OR CHEMICAL TREATMENT: The purification of water via chemicals is easy, although not as fast as the other methods. There are two types of chemicals that are commonly used in water purification: Iodine and Chlorine Dioxide. Bleach can also be used, but is not recommended and taints the taste of your water. Chlorine Dioxide is used in most chemical water treatment plants. Iodine is NOT effective against Cryptosporidium, however, and is probably best kept as an emergency backup. Iodine should also not be used by pregnant women, anyone with thyroid problems, or for an extended period of time.
The chemical is most water purification drops is Chlorine Dioxide. It is highly effective against bacteria and viruses, and mostly effective against protozoa. It also doesn't have an unpleasant aftertaste like Iodine does.
There are also treatment drops that use mineral salts to create oxidants in the water (such as Chlorine), which kills anything harmful. My chemical purification of choice is Purizine, which is a little bottle of mineral salt drops. There is no aftertaste, and you only have to wait an hour. Some chemical purification products including Purizine also contain coagulants, which bind large particles together so that they sink to the bottom and can be filtered out easily.
The one downside to chemical purification is that it takes time. It can take anywhere from fifteen minutes to four hours for water to be considered safe, so make sure you read the instructions. However, if you can afford to wait, this is the lightest and easiest method of water treatment on the market.
BOILING: Water can be boiled for at least one minute (at least three minutes at altitude over 6,000') to kill protozoa, bacteria, and viruses. This also helps any sediment to settle to the bottom of the pot, but won't help with cloudy water or any funny tastes that may be present. This requires a decent sized cook pot and a lot of fuel. I don't recommend it, except in cases of emergency.
IMPORTANT: WHEN USING ANY OF THESE METHODS, YOU MUST FOLLOW MANUFACTURER'S RECOMMENDATIONS FOR THE TREATMENT METHOD TO BE EFFECTIVE. Enough said.