Merit Badge Madness: Water Filtration and Purification

Keeping scouts hydrated

It is vital that your scout maintain proper hydration on all outings. This means he needs a constant supply of good clean water. For normal day hikes this can be accomplished with a 2 or 3 liter hydration pack (like a CamelBak) and maybe a water bottle or two.

For longer hikes or overnight adventures or where the water weight makes it impractical to carry enough clean water, It is imperative that he has a way to refresh his water supply. Refreshing his water supply in the wild is something he must get right, doing it wrong is not an option and can lead to short and long-term illness or worse. Have your scout practice filtering and purifying water at home so he can become familiar with the process. Further, your scout needs to understand that he must not wait until he is thirsty to begin gathering and preparing clean water.

How long can you go without water?

Depending on the level of activity, and ambient temperature, a person can survive only about 3 days without water. However, after prolonged activity without proper hydration your cognitive ability will begin to decline and your ability to make rational decisions will fade. Finding a way to create and maintain a source of clean drinking water is essential.

Do I really need to filter and purify the water?

Even in the back country of North America you can no longer trust clear mountain springs according to tests performed by the CDC. Most water found in the wild today should be considered unsafe without purification. If you gamble and drink directly from a contaminated source you will get sick, further dehydrating yourself, worsening your situation, and shortening your rescue timeframe.

What contaminants do I need to be worried about?

Water can be unsafe to drink due to a wide range of contaminants, the following list is the most common things that will make you sick. In this list I have included the average size of the bacteria and viruses for your reference. This information is important so you can understand what a filter can and can not do. As a comparison a grain of table salt is ~300 microns, a grain of powdered sugar is ~80-100 microns, a grain of icing sugar is ~20-25 microns, and the width of a human hair is ~30-100 microns.

Protozo:
- Giardia Lamblia: 8-12 microns
- Cryptosporidium Parvum: 4-6 microns
Bacteria: 0.2-4 microns
- E. Coli, Salmonella, Campylobacter, Shigella, etc.
Viruses: 0.004-0.1 microns
- Enteric, Hepatitis A, Norovirus, Rotavirus, etc
Chemicals / Poisons:
- Arsenic, Lead, Nitrates, Pesticides,
  Radium, Radon, etc.

Difference between filtration and purification

Filtration and microfilteration is the act of passing water through a filter with an absolute pore size to remove as many contaminants and bacteria as possible. Filters and micro-filters usually do NOT protect against viruses as they are too small relative to the pore size of the filter. In fact, some bacteria when turned just right, can pass through some filters.

Purification is the step taken after you filter, to remove any remaining bacteria or viruses. It is important to note that most purification steps require clear and relatively warm water to be effective. Dirty, cloudy, and or cold water is hard to purify, so filter as much as possible first.

Steps to effectively filter and purify your water

Find the best source of water you can. When looking for water choose running water in direct sun light over standing water in the shade. The higher the elevation, the safer the water, also take water upstream from meadows or fields where livestock or animals might graze.
Collect Water in a secondary container or disposable water bag if possible so you do not contaminate the sides and threads of your “clean” water bottle. If you only have one water bottle, then use a drinking straw to prevent cross contamination from the sides or threads of the water bottle. Let your collected water stand for 30 minutes or more to allow heavier particles to fall out of the water suspension.
Pre-filter the collected water as much as possible by pouring the water through a pre-filter or using a pre-filter around the intake hose of your main filter. Doing this will remove most of the sediment that can shorten the life of your more expensive main filters and will greatly assist in the purification step. A piece of cloth, coffee filters (20 micron pore size) with proper support, and commercial pre-filers are available and can be used in this step. Coffee filters, however, that are not properly supported will rip and tear under the weight of the water. Any pre-filter you use should be rated to at least 10-20 microns.
Filter with a high grade water filter that is rated down to an “absolute” pore size of 0.1 microns or smaller. This will remove the protozoa and most bacteria. Depending on the effectiveness of the device, and how small of a pore size is, the filter may also remove some viruses. If you have a carbon filter on the egress hose, you will be able to also remove some chemicals, organic chemicals, odors, and bad tastes from the filtered water.
Purify the water by either (NOTE: it is always good to have 2 methods of purification, one as a primary and one as a failsafe backup.):
1. Preferred Option - hard boil the water for 3 minutes at high altitude. Bacteria and virus begin to die in water over 160 degrees, but at that temperature it would take over 30 minutes to kill them. Boiling the water will also reduce the amount of air in the water, making the water taste flat and potentially metallic depending on the mineral content of the water. Pour the water back and forth between clean containers (not the container you collected the water with) or shake the water in a half way filled sealed clean water bottle to aerate the water.
2. Secondary Option - use a UV light, like a SteriPen or a electrolytic purifier. UV lights do NOT work well if the water is cloudy, so make sure you have clear water. UV manufacturers recommend that a 1 micron (absolute) filter be used with a UV System as the outer layer or shell of a Giardia Cyst is extremely difficult to penetrate with UV light.
3. Tertiary Option - use chemical treatments like Chlorine Dioxide. Chemical treatments do not work well with cold or cloudy water, so make sure the water is clear and warm. Make sure you follow the manufactures instructions and that the chemicals have not expired (if they are expired they are useless). The colder the water the longer it takes for the chemicals to work. So try and warm your water by putting it inside your coat or letting it sit in the sun.
Enjoy the clean water only after it has been fully purified. Remember that the container you used to collect the water may have contaminated edges or screw threads that you do not want to put in your mouth, so use a straw or drinking tube.