I always have three methods of purification in my Bushcraft Bag.
- Filtration
- Boiling
- Chemical Disinfection.
Let’s start with filtration, which is the method I use most. The filter I use is a Sawyer Mini water filter. Pros: Easy to use just fill squeeze bag and squeeze through the filter into another container. It is small, weighing two ounces and is 1 inch wide by 5 inches long. It filters 100,000 gallons, which for me is a lifetime in the field. It removes 99.999% of Protozoa and Bacteria. It costs me less than 20 dollars ($15 at Walmart). It comes with a tube that allows for drinking out of cracks and shallow pools, you just need to use the filter and tubing as a straw. You can also put it in line with your hydration bladder. Just put dirty water in the bladder put the Sawyer Mini in line with the drinking tube and suck clean water through the tubing. The syringe provided does two jobs backflushing the filter and it can be used to irrigated wounds (First Aid). Especially if you are using chemical disinfection, just use the normal amount of disinfectant and 1/3 the amount of water. Cons: The squeeze bags that come with it are somewhat fragile, but you can buy extras. You can also use empty Smart Water bottles in place the squeeze bags because they have the same threading as the filter. The filter requires back-flushing when using murky water due to clogging. I backflush with the syringe provided at the end of the day. You have also have to worry about it freezing and not working. Putting it in a shirt or pants pocket will help it thaw. If you do not have a Sawyer Mini you need one, unless you already own another filter.
Boiling is my second favorite method of water purification. If I am going to be drinking a hot beverage then just boil the water and skip filtration with the Sawyer Mini. To boil I use my Klean Kanteen 40z water bottle with the cap removed and my GSI Glacier Cup put over the mouth of the water bottle with the Cup upside down (like a lid) and put over the fire. I bring to a rolling boil for 1 minute if the water is not relatively clear or 10 minutes if the water is murky. I can also fill the Klean Kanteen and Glacier Cup both with water and bring them to a boil. The first method protects the water from having a smokey flavor because I have no lids. It is not often mentioned that you need to filter particulate out of the water because if bacteria, viruses, and protozoa are inside this floating debris the heat from a 1-minute boil may not disinfect your water. Pros: You have to carry a container to carry your water make it metal and you can boil in it. If you put cotton material or vegetable material in the Klean Kanteen with the GSI Cup over it as a lid you have a method for making charred material for fire making. Boiling water kills bacteria, protozoa, and viruses. If you expect human fecal contamination in your water boiling is the only safe option. Cons: You need fire or a heat source which is not always easy, convenient, practical, possible, and/or legal. I wrap rubber bands around the Klean Kanteen bottle to keep it from rattling when it nests inside the GSI Glacier Cup.
Chemical Purification is my least favorite method and, I use a Tincture of 2% Iodine. I start by filtering my water through a piece of cloth. I then add 5 drops of iodine if the water is clear and 10 drops if the water is cloudy. I wait a whole hour for the iodine to d its work. Chemical purification takes longer if the water is cold, so I wait an hour the maximum time it takes iodine to do its work at any temperature. Pros: I can use a 2% Tincture of Iodine for first aid. Cons: Wait time. It does not work against parasitic worm eggs and cryptosporidium. It is only low to moderately effective against giardia. It also is supposed to taste bad. The bad taste can be masked by drink mixes. The cons make this awater purification method of last resort for me.
I am going to change my chemical purification method to disinfect water to Chlorine Dioxide. It is the most effective method of chemical purification, but you have to wait 4 hours for it to work. So even with this change to Cholrine Dioxide chemical purification will always be a method of last resort for me.
Clarke's Bushcrafting and Survival 