How to Purify Water

How to Purify Water

When the water you're hoping to drink might be riddled with parasites or bacteria, you can't afford to skimp on water purification. In the very circumstances that put you in contact with questionable water (being in the wilderness, surviving or recovering from a disaster, or living in a part of the world where water isn't purified for you) the last thing you want to do is to get sick. Read the following instructions carefully and always be prepared to purify water yourself.

Step 1 A typical water container styleClean the containers in which you're going to hold or store the water. Use dish soap and water. Rinse thoroughly. After washing the containers, submerge them in a solution of 1 teaspoon of non-scented liquid household chlorine bleach to every quart (or liter) of water (making sure the entire surface of the bottle comes in contact with the solution for a minimum of 15 seconds), then rinse thoroughly with a weaker mixture of bleach and water.

NOTE: Don't use any container that has had milk or fruit juice in it. Milk protein and fruit sugars remain in the container and can fuel bacterial growth when water is stored. Plastic soda bottles are suitable.

Step 2 Filter water through a clean cloth. Then allow it to settle for at least 30 minutes and pour off the clear water for purifying. This process of filtering and settling is especially important if you're going to be using chemical purification because disinfectants are less effective in cloudy, murky, or colored water. It is possible to use cotton cloth, such as a clean handkerchief or clean white sock, or silk (water passes quickly through multiple layers). One way to set this up is to cut the bottom off of a water or coke bottle. Roll a clean sock up on itself and stuff it down to the neck of the bottle. Pour your water through the filter until it is clear to the eye.
If you have a portable water filter, use it.

Step 3 Speed up the clearing of water. One way to do this is to add a little alum (aluminum sulfate). This causes impurities to coagulate, which are removed as the particulate settles to the bottom of the container.

Step 4 Purify the water using any of the following methods. If you can, combine boiling with a chemical disinfection method; the boiling is more thorough, but the chemical method will continue to keep the water safe when it's stored. Select a method:
Boiling: This kills most types of disease-causing organisms and is the most recommended purification technique. Boil the water for 1 full minute, then let it cool. Make sure it's a full, rolling boil. If you are more than one mile above sea level, boil for 3 minutes longer.

Disinfecting: Disinfecting with household bleach kills some, but not all, types of disease-causing organisms. The bleach must contain chlorine in order to work. Don't use scented bleaches, color-safe bleaches, or bleaches with added cleaners. Most household chlorine bleaches have 4-6 percent available chlorine, in which case add 1/8 teaspoon (8 drops) of regular, unscented, liquid household bleach for each gallon of water (2 drops per litre), stir it well and let it stand for 30 minutes before you use it. Check the label; if the percentage of available chlorine is around 1 percent, or you don't know what the percentage is, use 40 drops per gallon/ 10 drops per litre; if the percentage is 7-10 percent, use 4 drops per gallon or 1 drop per litre. Double the amount of chlorine if the water is cloudy, murky, or colored, or if the water is extremely cold. If, after sitting covered for 30 minutes, the water doesn't have a slight chlorine odor, repeat the dosage and let sit for another 15 minutes.

Granular calcium hypochlorite: This works in the same way as household bleach. You can dissolve one heaped teaspoon of high-test granular calcium hypochlorite (about 1/4 ounce) in two gallons of water (1 heaped teaspoon or 7g for every 7.5 litres or 1 gram for every litre of water) to make a disinfecting solution. Then add one part of the disinfecting solution to each 100 parts of water to purify.

Potassium permanganate (KMnO4): This can be used to disinfect water. It can be purchased from camping supply stores and pool treatment stores. The water should be colored slightly pink, 3 or 4 crystals in a quart or litre of water. Let the solution stand for at least 30 minutes. This is definitely an emergency measure only, and should not be used for planned leisure activities, such as hiking or camping.

Disinfecting with iodine: This is generally less effective than chlorine in controlling the parasite Giardia, but it's better than no treatment at all. Add 5 drops of 2 percent iodine (from the medicine chest or first aid kit) to every quart or litre of clear water; add 10 drops if the water is cloudy. Let the solution stand for at least 30 minutes.
Commercial tablets: For commercially prepared chlorine or iodine tablets, follow the instructions that come with them. If you don't have instructions, use one tablet for each quart or litre of water to be purified.

Solar Water Disinfection (SODIS) method: Pouring the water into clear plastic PET bottles, and exposing to direct sunlight for at least 6 hours has been shown to be an effective method of disinfecting.

Step 5 Be careful with the cap or lid of the container. If you're chemically disinfecting water in a canteen or other portable container with a screw-on cap, wait about five minutes after adding the purifying chemical(s), then partially unscrew the cap and shake the container so that some of the water sloshes on the inside of the cap and the threads of the container, then re-tighten the cap and let it sit for the remainder of the time specified above or in the instructions. Otherwise, there may still be contaminated water in the cap, on the outside of the container's neck, or on the threads.

Step 6 Improve the flavor of purified water, if needed. Boiled water can taste "flat", and disinfected water can have a strong chlorine taste. Aerate it by pouring it from one clean container to another several times. Alternatively, add a pinch of salt to each quart or litre of water. If the flavor is still unpleasant, use a powdered drink mix, if available.

Step 7 Take care when consuming. Once the water in a container has been purified, open and close the container carefully. Don't touch the inside or the rim with your fingers, or else the water could become contaminated.
If you're going to drink some, but not all of the water, don't drink directly from the container. Pour it into another container and drink from that. Contact with your lips and mouth can contaminate water that's going to be stored.
If you don't drink the water immediately, write the date on the bottle. Store it in a cool, dark place for up to six months.


WARNING: All the methods indicated above are designed to remove biological threats only, such as bacteria. They generally do not remove chemical (for example, industrial waste such as aluminum sludge) or radioactive contamination. If it is suspected that the water contains such contaminants, rely on distillation, or weigh consumption against the risk of being dehydrated.
Chlorine and iodine can be toxic. Do not use a more chlorine than indicated, and use only in emergency situations.