The human body is about 60-70 percent water by weight. The amount of water a person needs per day varies depending on the temperature, humidity, altitude, and the amount of physical activity the person is engaged in. At rest, the Mayo Clinic estimates men need about 3 liters of water a day and women need 2.2 liters. But if you are exerting yourself in the mountains, that may increase by 50 percent, to over 4 liters for men, and more than 3 liters for women. At a weight of 2.2 lbs per liter, most of us don't want to carry enough water for a four-day backcountry trip in our packs (over 35 lbs for men, 26 lbs for women).
Fortunately, we can usually find the water we need in the backcountry from streams, lakes, snow run-off, or spring seeps. The problem is that backcountry water may not be safe to drink without treatment. Giardia, one of the more well-known risks to backcountry water sources, is a protozoan parasite readily transmitted via the feces of deer, cattle, beavers, and other mammals. But, other contaminants, such as bacteria, cysts, and a particularly nasty protozoan called Cryptosporidium, are also a risks, although small, in North American backcountry areas. And, internationally in developing countries, virus contamination is not uncommon and one could encounter viruses like Norovirus/Norwalk, Rotavirus and Hepatitis A.
The solution is to carry a backpacking water filter treatment device that can remove these contaminants, and simply cleanse water as you need it. Carrying a water treatment system is much lighter than bringing all the water you need. And with it, you need only carry enough water to get you from one source to the next.
Types of Water Treatment Systems
In this review, we examined 17 different backpacking water filter treatment systems to find the very best. Five different types of systems were represented:
Pump Filters — These are very common, and what people usually think of first when they think of water treatment. These devices cleanse water by pumping it through a filter that has a pore size that is too small for bacteria and protozoa to move through. Example: Katadyn Hiker Pro.
Gravity Filters — These products cleanse water by using gravity to push it through a filter, eliminating time-consuming pumping. Example: MSR AutoFlow Gravity Filter.
Filter Straws — These models treat water as you drink directly through a big straw, which doubles as a hollow fiber filter. Example: LifeStraw.
Chemical Drops and Tablets — Drops and tablets purify water by adding a chemical to it in order to kill all things living in the water. They have the advantage of killing viruses in addition to bacteria and protozoa. Example: Aquamira Water Treatment Drops.
UV Light — These mechanical devices purify water by zapping it with ultraviolet light. This also has the advantage of killing viruses. These products require batteries and/or chargers to work. Example: SteriPEN Ultra.
Why Treat Water?
First of all, what are you even trying to eliminate from your water with a treatment system, and is it even necessary to treat water? Recent research has concluded that backcountry sources at high elevations are probably cleaner than we once thought. It may not be necessary to treat all water that you come in contact with. The clincher? It is impossible to tell by sight if water is contaminated (unless there is an obvious contaminant present). A good rule of thumb is that if you are at a high elevation where there is no cattle grazing, no pack animals, and little human traffic, then you are probably all right. However, if you are along a heavily traveled trail, it is wiser to treat your water than to risk it. What are the risks? Here is a list of water-borne pathogens that could cause some serious intestinal tract discomfort.
Protozoa: This group includes the most commonly feared of all waterborne illnesses - Giardia and Cryptosporidium. These are single-celled parasitic organisms that cause intense intestinal problems, with symptoms appearing anywhere from two days to two weeks from ingestion. These organisms can live in cold water for weeks or months at a time. Cryptosporidium has a hard protective outer layer, which makes it resistant to many types of water treatment.
Bacteria: E. coli, Dysentery, and Campylobacteriosis, as just a few examples, can also live in water. These are the easiest pathogens to filter out and treat, since they are much larger than viruses.
Viruses: Examples include Hepatitis A and Rotovirus. Viruses are not thought to be a large threat when hiking and traveling in the U.S. and Canada, but on other international trips, viruses become a much larger concern. Viruses are extremely small, so they are not strained out with most filters, unless their pore size is as small as .02 microns.
Once you are aware of the risks of water-borne pathogens, the next step is learning how to prevent these illnesses.
Purifiers vs. Filters
Filters and purifiers have technical differences in effectiveness. A filter mechanically pushes water through an actual filter, straining out bacteria and protozoa, but typically does NOT kill viruses. A purifier is a system that is approved for eliminating viruses as well as bacteria and protozoa, and usually involves chemicals, though UV light functions as a purifier as well. There are now a few filters that also qualify as purifies such as the MSR Guardian and the Aquamira Frontier Max An example of a filter that does not treat viruses would be the Katadyn Hiker Pro, and a purifier would be the Aquamira Water Treatment drops.
What System Works on What Pathogen?
Unfortunately, there is no miracle system that is the perfect solution, though some systems come pretty close. Often, manufacturers recommend carrying a filter AND a chemical treatment because that is the fastest and most efficient way to eliminate all harmful possibilities from the water. Here is our quick and easy breakdown of what types of systems kill what types of pathogens and vice versa:
Effectiveness of Systems
Filters: Eliminate bacteria and Cryptosporidium, but traditionally not viruses. They strain out particulate and usually improve the taste of the water. Most filters have pore sizes that are not small enough to filter out viruses, but the Guardian has an extremely small pore size and does filter viruses.
Chemical Treatments: Eliminate bacteria and viruses, and can eliminate Cryptosporidium usually only after extended incubation time, (although not all chemical treatments claim to eliminate cryptosporidium, check the label) does not strain out particulate, and usually negatively affects the taste of water.
UV Purifiers: Effective against all pathogens: bacteria, viruses, and protozoa. UV treatments do not actually kill pathogens, they simply scramble the DNA of the organisms so that they cannot reproduce. UV purifiers do not strain out particulate unless you use a pre-filter. They also do not change the taste of the water. One other noteworthy detail is that the EPA approves of the UV process as a purifier, which is used in many large commercial water treatment plants. However, the EPA does not actually approve specific UV devices that hikers carry.
What Eliminates Certain Pathogens?
Cryptosporidium: Filters eliminate, UV purifiers effectively disable, chlorine dioxide tablets eliminate after four hours and drops after one hour, iodine does not work.
Viruses: Eliminated by iodine, chlorine dioxide, and UV purifiers, but only a small number of filters.
Bacteria: Eliminated by all systems: filters, chemical treatments, and UV purifiers.
Particulate: Okay, so this isn't a harmful pathogen, but silt and dead bugs do not make for appetizing water. Filters, or separately purchased pre-filters, are the only things that strain particles out of your water.
The Effectiveness Bottom Line
So now that we have laid it all out for you, what does that mean you should choose? The absolute safest way would be to combine a chemical treatment, such as Aquamira, with a lightweight filter such as the Katadyn Gravity Camp. This means you can quickly strain out particulate and Cryptosporidium, but the chemicals can also eliminate viruses. However, carrying two systems is unnecessarily heavy and complicated.
Take into consideration where you will be traveling. Hiking through the High Sierra? You would probably be fine with just one system, either a filter or chemical, because the water there is clear and relatively clean. Filters are thought to be adequate for backcountry travel in the U.S. and Canada. Traveling internationally? You will want something that kills viruses, so ditch the regular filters and either bring along the MSR Guardian, he SteriPEN or a chemical treatment to make sure you eliminate all pathogens.
Other User Considerations
After effectiveness, the primary concern of a hiker is how much the treatment system weighs. Common systems have drastic variance in weight, ranging from a couple ounces to over 22 ounces. Depending on your activity, weight can be of more or less concern. If you are hiking long distances, we suggest a small and light chemical method, such as Aquamira Water Treatment Drops. If you are traveling internationally, especially to developing countries and are setting up a base camp, a heavier but highly effective method such as the Guardian would be an ideal choice. For the average hiker in the U.S., we suggest a filter, either gravity-fed like the Platypus GravityWorks or a pump like the Katadyn Hiker Pro, because these are effective without being too heavy and also do not involve adding chemicals to your water and your body.
Time Before Drinking
The time it takes for different methods to treat drinking water varies wildly, from 90 seconds for a liter from the SteriPen Ultra to half an hour for Aquamira Treatment Drops to 40 seconds for the Katadyn Gravity Camp 6L. If you are on any kind of backpacking trip, whether it's a weekend trip or a thru-hike of the entire Pacific Crest Trail, time is of the essence, and you will not want a treatment method that takes a long time. For a personal filtration system, the Sawyer Mini is an immediate system to get water into your body.
If you are just looking for an emergency treatment method to leave in your pack, a chemical treatment would work fine or something like the inexpensive Lifestraw. In general, filters, either gravity-fed or pumps, work faster than chemical treatments, although chemical treatments are lighter and smaller to pack. UV treatments are also quick.
Other Filter Details to Consider
Ability to Treat Large Quantities of Water
If you are a single hiker on a short trip, then this is not a huge concern. Scooping water into your Nalgene and treating with a SteriPEN will work just fine. However, if you are bringing one treatment method for a group of people, or you want the ability to treat a lot of water for cooking at base camp, or there are limited water sources so you need to be able to collect and treat a lot of water at once, it is worth taking into consideration how to treat a lot of water. In these situations, collecting and treating water with the SteriPEN one bottle at a time is tedious and inefficient. Pump filters work well in these scenarios because they can easily treat as much or as little water as needed. The gravity-fed filters excel in this area and have the ability to collect and treat a lot of water quickly, which is great for groups.
The filter is the actual material that catches the organisms in your water, and there are multiple types on the market. Here is a brief list of the types:
Ceramic: This is an earthen material (yes, the same kind of stuff your favorite coffee mug is made out of) that has a long life and can be cleaned many times before being replaced. Unfortunately, it can get clogged easily. But on the bright side. it is easy to scrape clean. Ceramic filters can also come with a carbon core, which helps to remove chemicals from water. Example: MSR Miniworks EX.
Fiberglass: A material that is more fragile than ceramic, but still effective at eliminating particles. Example: Katadyn Vario.
Hollow Fiber: Made up of hollow U-shaped microtubes, this filter allows water through tiny pores and into the core, where pathogens are strained out.
Silica Depth: Using finely grained silica sand, this filter works by having multiple levels of different sized grains, going from largest to finest. It catches different sized particles and organisms as water is pushed through its levels of density.
If you are shopping for a filter, a techy detail that you will continually stumble across is micron size. This is a measurement of the pore size in the filter media. Essentially, the smaller the pore size, the more pathogens the filter can strain out. A simple rule of thumb is that the smallest bacteria is 0.2 microns, so a filter should be around that size or smaller to be the most effective. Now filters are coming on to the market with a pore size of .02 to be effective against viruses we think the Aquamira Frontier Max has this pore size but is incredibly slow — we suspect in part because of this small pore size, however other manufacturers like MSR and their Guardian have figured out how to make that process much faster with the same micron size.
Durability/Uses Before Maintenance
If you have chosen a pump filter as your treatment method, and you plan to bring it with you on multi-day trips, it is important that you look for a pump that is field maintainable, meaning you can service it on your own in the backcountry if it gets clogged. For example, ceramic filters need to be scraped relatively often, but this is easy to do. Most other pump filters are engineered to be easy to back-flush to remove clogs, but it is worth investigating how complicated this process will be so you don't get left high and dry on your over-nighter.
It is also worth noting how long a filter will last before it needs to be replaced. Ceramic filters can filter up to 2,000 liters, while other types of filters may only be effective to around 500 liters. You can purchase replacement cartridges once the filter has run its course.
Electronic treatment methods such as a UV purifier have an entirely different concern: battery life and bulb life. UV lamps typically last around 8,000 treatments, which is excellent life. However, batteries need to be replaced or charged every 40-100 treatments.
Advice From Thru-Hikers
For those of you ultralight or long distance hikers, we talked to some Appalachian Trail thru-hikers to see what their thoughts were on water treatment methods, and ultimately what they prefer to use.
The most important features to a long-distance hiker striving for a light pack are not all that different from our general considerations: weight, the time it takes to treat a liter, price, and upkeep. Not surprisingly, they said all the filters were too heavy and they would not consider carrying them. Initially, the SteriPEN was an attractive option, but the lithium batteries didn't last long, were expensive, and were hard to find in towns along the Trail. The most popular method along the trail was by far Aquamira Water Treatment Drops. This system is incredibly light, inexpensive, and can be used over the long-term, with many hikers finding it ideal. Thru-hikers may want to take a closer look at systems like the Sawyer Mini or Lifestraw Flex they're light and allow you to drink directly out of them. If you anticipate being near water most of the day you could avoid carrying any water and just drink on the fly.