5 Best Methods for Purifying Water in Survival Situations


Best Methods for Purifying Water

Purifying drinking water is probably the most critical piece of knowledge for backpackers, hunters, or anyone in even the most basic survival situation. It is vitally important that you have a solid understanding about the different methods for purifying water. Water is needed for just about everything, and if you know the basics of purifying the water you find, you’ll be miles ahead of the average person. Any local stream, water reservoir, or lake will become a critical resource that you can use to ensure your survival.

Importance of Knowing How to Purify Water

In a major disaster where the basic utilities that you rely upon in your daily life are not available to you, knowledge of self sufficiency will be critical. Food and water are most critical to your survival. Humans can last a few weeks without food but only a few days without water. If you can secure a means of acquiring fresh water, then you just bought you and your family a whole lot of time figure the rest out.

So why can’t you just drink out of a stream if you needed water? Well that’s because of bacteria, viruses, and chemical pollutants. Something as simple as deer droppings up stream from where you get your drinking water could get you seriously ill or even kill you.

Diseases that can result from drinking unpurified water include Giardia, Cholera, Typhoid Fever, E-Coli, and Dysentery. These are all very serious diseases so always ensure that you are drinking  water that is safe.

5 Methods for Purifying Water

MethodBasic Instructions
Boiling Water
  1. Filter or strain the large particles from the water.
  2. Bring water to a boil for 1 minute (for elevations up to 6500 feet) or 3 minutes (for higher elevations).
  3. Let the water cool.
  4. Drink.
Bleach
  1. Filter or strain the large particles from the water.
  2. Add 16 drops of bleach per gallon of water (or 4 drops per liter).
  3. Mix thoroughly.
  4. Let the water stand for 30 minutes.
  5. Make sure the water has a faint chlorine smell.
  6. Drink.
Water Filter
  1. Put intake into the water source.
  2. Pump or push water through the filter element.
  3. Collect the filtered water.
  4. Drink.
Iodine
  1. Filter or strain the large particles from the water.
  2. Add 5 to 10 drops of iodine per liter of water.
  3. Let the water stand for at least 20 minutes.
  4. Add a powdered drink mix for a better taste (optional).
  5. Drink.
Sunlight Exposure
  1. Find a clear plastic or glass water bottle.
  2. Remove any labels and make sure the bottle is as clear as possible.
  3. Fill with water to be disinfected.
  4. Lay bottle on a flat surface with direct exposure to the sun.
  5. Let it sit in sunlight for five hours.
  6. Shake water vigorously.
  7. Drink.

Where to Find Sources of Water

Sources of water can be found in many places both inside your home and outside. For water sources inside your home, consider checking what water remains in the water pipes, water heater, toilets, and fish tanks. For sources outside of your home, check for nearby lakes, ponds, rivers, or any other body of water. Of course most of these sources will require some method of purification in order to make them safe to drink. Below we will discuss the most common potential sources of water found outside the home and the quality of the water found in each source.

Potential Sources of Water Outside the Home

SourceSource QualityWhat You Should Consider
Standing Puddle
LOWStanding water is the least desirable source as the water is often a breading ground for organisms and insects. Puddles on the street are almost always contaminated with chemicals that have leached out of vehicles. Once the puddle is dried up it probably wont return until the next rains.
Slow Moving River Through Town
LOWWater is flowing which is much more desirable than standing water. This river is surrounded by urban developments making the risk of contamination very high. The water appears murky indicating a high number of particulates in the water. It appears to be easily accessibly by the public adding further risk of contamination.
Pond or Lake
MODERATEWater is standing and not flowing and could facilitate organisms and insects. This body of water appears to be open for public use which presents more of a risk of contamination. This source does appear to be large enough to provide a significant amount of water. Higher altitude bodies of water are generally cleaner as they are less likely to collect run off from farm lands or industrial sites.
Fast Moving Mountainous River
HIGHWater is flowing at a fairly fast rate helping to ensure the water is fresh. There is snow along the banks which indicates the water is probably snow run off.  Being at a high altitude helps to keep contaminants from upstream to a minimum. It appears to be fairly remote meaning human-induced contaminants are less likely.

Method 1: Boiling Water for Decontamination

Most survival types are very familiar with the fact that you can boil water as a means of making it biologically safe to drink. This is probably the most well known method for purifying water. Boiling the water will kill bacteria and any organisms that might be in it. This wont remove any chemical contaminants from the water but at least you know you wont be getting Giardia along with all of it’s nasty symptoms in the middle of a crisis situation.

It is also critical that you filter the large contaminants out of the water prior to boiling the water for drinking purposes. Even something as simple as a wet t-shirt folded over itself a few times can accomplish this. Pour the water through the t-shirt to ensure no large debris particles remain, then boil.

To Purify Water with Heat

  1. Filter or strain the large particles from the water.
  2. Bring water to a boil for 1 minute (for elevations up to 6,500 feet) or 3 minutes (for higher elevations).
  3. Let the water cool.
  4. Drink.

“Bringing the water to 160°F for a duration of 30 minutes or 185°F for 5 minutes has the same effect as bringing it to a boil.”

The Wilderness Medical Society

Not many people know that it isn’t even necessary to bring the water to a boil. According to the Wilderness Medical Society, bringing the water to 160°F for a duration of 30 minutes or 185°F for 5 minutes has the same effect as bringing it to a boil.

Boiling water for purification.
Boiling water as a means to make it safe for drinking is probably the oldest and most well known method of purification.

Knowing this can be a life saver in a survival situation. If you have a fuel efficient way to bring your water up to 160°F for 30 minutes, then you will have biologically safe water to drink. Preppers have accomplished this with things such as solar cookers. The downside to using this as a means to purify water is that (as stated above) it does nothing if there are chemical contaminants in the water. The water also needs to cool down prior to drinking it.

If you want to take further precautions to ensure your drinking water is safe for consumption, consider also performing the next method and treating the water with bleach.

For an in-depth explanation on purifying water with heat, see Boiling Water for Drinking: What Temperature and How Long.

Method 2: Purifying Water with Bleach

Purifying water for drinking using bleach is very practical and doesn’t take near the amount of energy to accomplish as boiling water does. With this method you can add a small amount of standard bleach to the water making it biologically safe to drink. Using the correct amount of bleach will kill any organisms in the water while still keeping the chlorine levels low enough so that it is safe for human consumption.

When you buy bleach for this purpose, make sure that the active ingredient is sodium hypochlorite (NaOCl) with a concentration of between 5.25% and 6%. Some manufactures add Sodium Hydroxide as an active ingredient as well which is safe and will not pose any health risk when using it to purifying water. It is critical to ensure that it is standard bleach with no additives (such as scented bleach).

Disinfecting Water with Bleach

  1. Filter or strain the large particles from the water.
  2. Add 16 drops of bleach per gallon of water (or about 4 drops per liter).
  3. Mix thoroughly.
  4. Let the water stand for 30 minutes so that the bleach can adequately disinfect the water.
  5. Make sure the water has a faint chlorine smell.
  6. Drink.

After the water has sat for 30 minutes, smell the water. If the water has a faint smell of chlorine, then you are done and can consume the water. If not, repeat the process by adding 16 more drops of bleach (or about 4 drops per liter of water), mix, and allow it to stand for 30 minutes.

If the water still does not have the faint smell of chlorine at this point, it is best to discard the water and find a new cleaner source. Once you are satisfied with the treatment of the water, you may want to aerate the water to assist in evaporation of the chlorine prior to consumption. This will also help the water to taste better. An easy way to do this is to pour the water back and forth between two containers a few times.

Research has shown that the colder the water, the less effective chemical treatments such as this are at purifying water. One study showed that at 50°F, chemical treatment left as much as 10% of Giardia particles alive in the water after 30 minutes of exposure to the chemical treatment. If you are in doubt as to if the water is at the optimal temperature, just allow the water to sit longer than the 30 minutes prior to consumption. Ideal temperature for the water for chemical treatment is at least 60 °F.

Note: Although not required, it is best to use the boiling and bleach treatment methods in conjunction to ensure maximum effectiveness with purifying the water. When doing this make sure you boil the water first, followed by the bleach method.

For an in-depth explanation on purifying water with bleach, see How to Use Bleach to Purify Water for Drinking.

Backpacker who found a water source and needs ways he can purify it.
Using light weight portable water filters is a favorite among back country backpackers.

Method 3: Use a Portable Water Filter

Small portable water filters were originally created for backpackers who spend days on end in the wilderness. When you are spending that much time away from the comforts of a running tap, you can’t carry the required amount of water with you, so you’ll need to find a way to purify what you find.

These filters have been a long standing solution to this problem and are great for survivalists and preppers alike. This type of filter uses a ceramic filter element to filter out the bacteria and other unwanted particles. It’s filter also contains carbon which will also remove most chemical contaminants as well. These are light and highly mobile. These types of filters will generally process hundreds of gallons and the modern filters are rechargeable. So you don’t need to buy new filters, just clean out the one you have.

Using a Portable Water Filter

  1. Put intake into the water source.
  2. Pump or push water through the filter element.
  3. Collect the filtered water.
  4. Drink.

Note: Each water filter is slightly different, always make sure you follow the manufacturer’s directions.

Top Emergency Water Filters

These are a great addition to any survival supply. There is not a lot of instruction to give on using one of these. You put one end in the water you want to filter and pump. The water that comes out is ready to drink. You can use this in combination with the bleach technique mentioned above but it’s really not required.

These filters will catch particles in your water down to 0.2 microns in size. Which means they should be able to filter out most trouble causing organisms in your water. Keep in mind that viruses are too small to catch with these filters (not much of a concern in remote areas). See the chart below for more info on the sizes of different microorganisms.

Harmful Microorganisms and Their Sizes

TypeExamplesSpore SizeType of Filter Needed
ProtozoaGiardia, Cryptosporidium5 microns or largerWater filter
BacteriaCholera, E. coli, Salmonella0.2 -€“ 0.5 micronsMicrofilter
VirusesHepatitis A, rotavirus, Norwalk virus0.004 micronsWater purifier

Compare the sizes of the above listed microorganisms to your water filter’s specifications to help you determine if it is capable of filtering out all harmful microorganisms from your water.

Method 4: Purifying Water with Iodine

Using Iodine to disinfect water does not seem to be terribly popular but it is a great skill to know how to do. Iodine is a great wound disinfectant, water purifier, and is very shelf stable. Iodine is often found in emergency medical kits and is extremely useful.

You will want an iodine solution called “Iodine Tincture” with a 2% USP content. “USP” refers to the concentration of iodine that is in the solution. The 2% solution is the most commonly available.

Using Iodine to Disinfect Water

  1. Filter or strain the large particles from the water.
  2. Add 5 to 10 drops of iodine per liter of water.
  3. Let the water stand for at least 20 minutes.
  4. Add a powdered drink mix for a better taste (optional).
  5. Drink.

Iodine is most effective in warm water. If the water is cold or suspected of having a high number of pathogens, allow the water to sit at least 30 minutes after adding the iodine. Also, you can increase the iodine safely to no more than 10 drops of iodine per liter of water. Adjust the number of drops and the exact time you allow it to sit after treatment based in accordance with how clean the water source is.

When you drink the water after treating it with iodine, you will notice the taste of iodine is still in the water. This is normal and does not indicate that the water is unsafe to drink. Although some people seem to be more tolerant of the taste of iodine treated water than others, most survivalists will still include powdered energy drink mixes along with their iodine so that it may be used as a means of hiding the iodine taste.

A few important notes about treating water with iodine: Iodine is sensitive to sunlight and should always be kept in a dark place and/or in a dark colored bottle. Also, avoid drinking iodine treated water if you are pregnant, allergic to iodine, have thyroid problems, are on lithium, or are a woman over 50 years of age. Some people allergic to shellfish have also shown an allergic response to iodine.

For an in-depth explanation on purifying water using iodine, see How to Purify Water for Drinking Using Iodine.

Sodis Method - Probably the most useful of all the methods of purifying water.
Villagers in Indonesia learning how to purify drinking water using only the sun and plastic bottles.

Method 5: Purifying Water by Exposure to Sunlight

The Ultra-Violet rays in sunlight is a natural killer of microbes in water. Therefor it is very possible to render water safe to drink merely by prolonged exposure to sunlight. This method is called SODIS, or Solar Water Disinfection. The World Health Organization has confirmed that the SODIS process works, after testing in multiple third world countries.

Using Sunlight to Disinfect Water

  1. Find a clear plastic or glass water bottle (the smaller the better, no larger than 2 liters).
  2. Remove any labels and make sure the bottle is as clear as possible.
  3. Fill with water to be disinfected.
  4. Lay bottle on a flat surface with direct exposure to the sun.
  5. Let it sit in sunlight for six hours.
  6. Shake water vigorously.
  7. Drink.

This method of disinfection water is a great technique to be familiar with since all you need is a clear plastic bottle and sunlight. Since the water needs to be exposed to sunlight in order to kill any organisms it contains, it is important to note that the larger the plastic container is, the harder it will be to kill any organisms inside. This is because the more water the sunlight needs to travel through, the less effective it is at killing organisms near the bottom.

It is important also, that you get the water as clear as possible. If the water is murky or contains lots of particulates, try straining it first through fabric or any other type of improvised filtration to get it as clear as possible. If you want this method to be as effective as possible, use small water bottles, as clear water as possible, and allow the temperature of the water to rise as much as possible during the process. Many people will lay the water bottle on a black metal surface in the sun to aid in raising the water temperature during this process.

For an in-depth explanation on purifying water using sunlight, see SODIS Method: Using Plastic Bottles and the Sun to Purify Water.

Conclusion

Probably the most important survival skill you can have is knowing multiple methods for purifying water. If you are familiar with these methods, you should be able to make water drinkable in even the worst of conditions.

Remember that you can always do a combination of these methods if you are really worried about the quality of water. Such as filtering the water first, and then chemically treating it. It is always better to spend a little extra time by treating your water twice rather than becoming ill during an emergency situation.

John Walter

John Walter is an emergency preparedness consultant with eight years of experience and training in related fields. He is a passionate prepper living in the Sacramento area of California.

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