In a survival situation, clean drinking water will often be your most important resource. A healthy human may be able to survive for a month or more without food but only for a few days without water.
A swift-flowing mountain stream might look like a good water source, but beware. Drinking water directly from a natural source in a remote environment could do you more harm than good. Unpurified water can contain bacteria, viruses, and microorganisms such as Giardia or cryptosporidium that cause intestinal problems including diarrhea, cramps, and vomiting. In some climates, you can also contract diseases (such as cholera and typhoid) or other parasites (such as flukes or leeches) from drinking unpurified water.
Here are three common methods to purify water in the backcountry or in other remote areas where you might not have access to clean drinking water:
Water Purification Method #1: Boil Water
What you need: Water, a container in which to boil the water, fuel, a heat source such as a fire or stove.
How to do it: Boil water at a rolling boil for between 5-10 minutes. Water may be safe to drink after as little as one minute of boiling, but boiling for longer can improve results. Increase boiling times for higher altitudes.
Pros and cons: In a survival situation, you might not have all of the tools you need, such as a container in which to boil the water. Even if you are able to find a natural fuel source and start a fire, you still need to either have or make a container in which to boil it. Boiling water is also a time-consuming way to purify drinking water. However, boiling water is one of the most effective ways to kill a variety of microorganisms, viruses, and bacteria.
Water Purification Method #2: Water Purification Tablets
What you need: Water, a container for the water, water purification tablets.
How to do it: Water purification tablet instructions vary, but generally you will simply open up a packet that contains a tablet, add it to the water, and then wait for a specified time before drinking. A small, pill-sized tab usually filters one liter of water and may require a thirty-minute wait; check directions on the type of tablet you have before using this method. Cold water temperatures may require longer wait times.
Pros and cons: If you failed you pack water purification tablets in your emergency gear, you simply won’t be able to use this method. However, if you do have them with you, they’re cheap, light, and effective. You can improvise your gear to make a container by lining a shoe with a foil emergency blanket, for example, while you wait for the tablet to purify the water. Tablets have a shelf life; make sure to check purchase dates, and replace them as needed.
Water Purification Method #3: Iodine and Bleach
What you need: Water, a container for the water, and either iodine or bleach.
How to do it: Per liter of water, add 3 to 5 drops of liquid chlorine bleach (such as a household bleach that contains between 5 and 6% chlorine), mix, and wait for at least thirty minutes for clear water. Or, add 5 to 10 drops of a 2% tincture of iodine to one liter of water, mix, and wait at least 30 minutes before drinking for clear water, or longer if water is cloudy.
Pros and cons: Again, you simply have to pack these items in order to have them available, but if you’ve included iodine in your first aid kit, you can also use it for water purification. Iodine and bleach may not be able to effectively kill Cryptosporidium and may not always kill Giardia. Filtering water through a portable pump filter before treating can increase effectiveness. Iodine and bleach often affect the taste of your drinking water; they require wait times, which are longer if the water is cold or murky. Pregnant women, people with an active thyroid problem, or those allergic to iodine should not use iodine to purify water.
Final tips: Filter dirt and debris from murky water by pouring it through a silk scarf or a piece of clothing before attempting to purify it. Several types of portable water filters and purifiers also exist in addition to the above methods of purifying water. Using a portable water filter in addition to one of the above methods can increase effectiveness in some situations. And, finally, if you anticipate needing to drink water from an outdoor source, plan ahead to procure your most important survival resource: clean, drinkable water.