Water Purification & Filtration 101

One of the most common and tragic mistakes amateur outdoor enthusiasts make is to underestimate the importance of proper hydration and backcountry water purification when planning their outdoor activities. Water is the Number Two most important ingredient after air for sustaining life and maintaining normal metabolism. For example, an average person needs about two liters of water per day under normal conditions. However, in hot weather, up to one liter of water per hour may be required. Many people underestimate this requirement and do not properly plan their water supply. Losing only 1.5-2% of bodily fluid can result in an inability to continue your trip, serious illness, or even death. Many avoidable fatalities, injuries, and ruined vacations result every year due to under-preparedness or unpreparedness by the unaware folk.

With this in mind, be prepared to take plenty of purified drinking water, even on minor outings. This is a situation in which being over-prepared can be a great benefit. If you are going on a multi-day backpacking or camping trip with a lot to carry, taking enough purified drinking water may be impractical, due to its weight and the space it would require. In this case, you may resort to filtering and disinfecting water from natural backcountry sources. Before you set out, research a route for available natural water. If there are several sources along your trail, you are good to go. However, before you go, research and decide which purification methods will work best for you. Many sources such as rivers, ponds, and lakes can be infested with harmful microbes, including bacteria, protozoa, algae, and viruses. These water-borne pathogens often come from waste contamination from animals in the area. The microbes are invisible to the human eye and cannot be completely avoided by choosing clear, fresh-tasting water. Harmful elements and microbes may also come from sources such as waste water and runoffs after storms. For this reason, choosing a proper water collection point that is least likely to harbor harmful elements is vital. Avoid collecting water from places that exhibit the following properties:

1. Eddies along river or stream banks with stagnant water
2. Shallow and warm water
3. Visible algae bloom
4. Strong “organic” odor.

On the contrary, fast streams, springs, and rivers usually have cleaner water and are a better choice of water supply. Prefer collecting water from:

1. “Flowing” portion of a stream or lake
2. As far from a riverbank or shoreline as possible.

After collection, water purification from dirt and pathogens can be done by taking the following steps: pre-treatment, filtering, and disinfection, or boiling. Pre-treatment is a process of removing sediment from the cloudy water because it will decrease the efficiency of further purification. Sediment usually consists of small solid particles that are suspended in the water and may harbor pathogens. To perform pre-treatment, one can use a coagulant such as aluminum sulfate (“alum”) or other commercially available types. When added to murky water, the coagulant attaches to suspended solids and forms small dense clumps, called “flocs,” that settle at the bottom of a container. Once all the flocs are on the bottom of your container, separate the clear water by carefully pouring it into a different container. Use the manufacturer's instructions to use a coagulant properly to remove sediment. In a pinch, straining the water through a bandana, clean sock, or T-shirt should remove the largest particles and prep it for further filtration. After removing sediment and suspended solid particles from collected water, it is ready to be treated for eliminating pathogens. Depending on where you are planning your trip, you may need to adjust this procedure to account for specific contaminants that are found in the area. The most common parasites are Cryptosporidium and Giardia Intestinalis. They can live in the intestines of humans and animals and cause serious intestinal distress and cramps. Here is a list of some methods that may eliminate parasites, in the order of their effectiveness.

1. Boiling water for at least 1 minute, at sea level, is a very effective method for eliminating a variety of microbes.

2. Proper filtration is highly effective in removing Cryptosporidium and Giardia cysts when using filters with an absolute pore size of 1 micron or smaller. According to this guide from the US Center for Disease Control and Prevention (CDC), filters should adhere to the National Sanitation Foundation Standard 53 or 58, with explicit statements such as “cyst reduction” or “cyst removal.”

3. Disinfection with chlorine is not effective in killing Cryptosporidium and has a low to moderate effectiveness in killing Giardia. Disinfection with chlorine dioxide has a high effectiveness in killing Giardia, but has a low to moderate effectiveness in killing Cryptosporidium.

4. Disinfection with iodine or chlorine is not effective in killing Cryptosporidium.

Boiling water is the most effective disinfection method for backcountry water, but it may require large amounts of fuel and extra tools. If you resort to boiling water, keep in mind that water boils at 212˚F at sea level. Clear, pre-treated water can be considered completely free of disease-causing microbes after being boiled for at least one minute at sea level. However, as elevation increases, both the atmospheric pressure and the boiling temperature decrease, which requires longer boiling times to kill all microbes. For each additional thousand feet above sea level, an additional minute of boiling time must be added, as follows:

1. One minute at sea level

2. Two minutes at 1,000' above sea level

3. Three minutes at 2,000' above sea level

4. Four minutes at 3,000' above sea level

While boiling could be the most comprehensive method of water purification, it may require more time to set up, large amounts fuel, extra accessories that add weight, and additional time to cool down. Filtering water can be a more time- and fuel-efficient method for effectively removing large parasites. However, filtration systems remain more of a mystery to many amateur outdoors enthusiasts and, therefore, are worth discussing in more detail.

There two most common types of filters are gravity and pump. Gravity filters typically consist of a flexible polymer water reservoir and a filter cartridge, which is usually attached at the bottom. As implied by its name, gravity filters are passive devices in which water flows down under the pull of gravity through a filtering cartridge into a “clean” collection reservoir. These filters require less work on your part because they just can be filled with water and hung on a tree or a tent pole to do their job. You may find that gravity filters are more convenient in places where water is easily reachable and can be readily scooped from a bank into a reservoir.

Gravity Filter	Pump Filter

In contrast to gravity filtering systems, pump filters require active pumping to perform filtration. They usually consist of a pre-filter attached to a collection hose, filtering unit with a cartridge, a pump, and a hose or faucet. You need to put in time and effort to force water through the filtration element, but this can be more effective for water sources that are not easily reachable without the pre-filter hose, such as rivers, lakes, or ponds with high or rocky banks. You can just drop the pre-filter hose into the water and start pumping.

Differences aside, these two filtering systems share a common main component that determines the effectiveness of the entire system and the final quality of the filtered water: the filtering cartridge. Filtering cartridges may employ different materials or technologies, but are essentially intended do the same thing—filter out fine sediment and microbes to make non-potable water safer to drink. When selecting a filtering product, look for two things in the manufacturer's literature: what agents they can effectively remove from water, and how easily they can be maintained and cleaned in the field. It is preferable to use filters with pore sizes that are smaller than 1 micron. This allows the filter to remove most large bacteria and protozoan cysts, which tend to be 1 micron or larger in diameter. Many models even advertise that their systems have membranes as small as 0.2 microns. If their claim is true, then these filters are capable of filtering out most bacteria and parasitic cysts from outdoor water. As stated above, the CDC advises that filters must meet NSF 53 or 58 standards, with explicit statements like “cyst reduction” or “cyst removal” to achieve acceptable removal levels of Giardia cysts and of Cryptosporidium oocysts. If a filter meets this standard, this should be indicated either on the label or in the manufacturer’s specifications. Beware, however, of statements that claim to remove viruses. They are much smaller than bacteria: 0.02-0.4 micron, so they are too small to be filtered by those filters that have 0.2-micron pores.

Filtering element with pores smaller than 1 micron	Filtering element with pores greater than 1 micron

Backcountry water sources may contain other small, exotic microörganisms, so a thorough disinfection may need to follow the filtration process. While pretreatment and filtration remove sediment and tough parasite cysts, disinfection destroys many of the smallest pathogens that may pass through these filers, like small bacteria and viruses. The two most common disinfectants used to treat drinking water are chlorine or iodine-based. Because it is more effective, chlorine is the most widely used disinfectant for water treatment, but it takes at least 30 minutes to fully disinfect—which is known as the “detention” time or “contact” time. Iodine-based disinfectants can partially disinfect water, but are not as effective at killing intestinal viruses or other pathogens as chlorine-based disinfectants or boiling. When using these chemical-based disinfectants on your trip, it's important to make sure to follow the manufacturer’s instructions carefully, to achieve effective water disinfection. With both chlorine and iodine disinfectants, it is critical to pre-treat water in order to remove sediment and organic matter, which may protect microorganisms from chemical treatments and prevent a complete disinfection.

Despite the many unpleasant surprises that being in nature may present, you can enjoy fun and memorable trips with your friends and family if you prepare thoroughly. Keeping yourself well-hydrated and having proper purification methods and filtration gear handy will definitely give you the right start. Just remember:

1. Don’t underestimate the importance of drinking plenty of water while outdoors.

2. Calculate how much water you will need, err on the side of caution, and overestimate your needs. This is a case where there is no such thing as being “over-prepared.”

3. Do your homework and find out if there is water where you’re going. Find out how safe it is, then decide whether to bring water with you or use a backcountry supply.

4. Know which purification methods will be adequate for your route.

5. Choose filtration systems that will work effectively with the pathogens you may encounter.

6. Use a combination of filtration and disinfection with sources that may have several types of microbes.

7. Boil any questionable water as the primary way of making it safer to drink, and use comprehensive filtration/disinfection only if boiling is too inconvenient or impossible.