With a few exceptions, like rain water and water collected through a solar still, the water collected from most water sources in a survival situation will need to be treated before it is safe to consume.
If you don’t have a device that filter and disinfects the water, you will have to accomplish the same task in two stages. Before purifying the water, you will have to filter it to remove any debris.
Filter Frame or Tripod Filter
If you are not carrying a filtration system with you such as a “Lifestraw Personal Filter”, you could construct an improvised water filter. A water filter frame or tripod filter uses pouches of contrasting natural materials to remove unwanted particles from natural water. Pour the water into the uppermost pouch, and allow it to filter slowly down into a container at the bottom.
This water filter is a three tier system. The first layer, or grass layer, removes the larger impurities. The second layer, or sand layer, removes the smaller impurities. The final layer or charcoal layer (not the ash but charcoal from a fire), bonds and holds the toxins. All layers are placed on some type of straining device and the charcoal layer should be at least 5-6 inches thick. Layers should be changed frequently and straining material should be boiled. Remember, this is not a disinfecting method, cysts can possibly move through this system.
A hanging water filter works in the same manner as the filter frame or tripod filter, by allowing the water to pass through the layers of filtration. The contrasting layers of rock and sand inside the cloth bag or bottle will each strip particle of debris from the water, leaving in clean enough to be bottled for purification.
To make a hanging water filter you can either use a piece of cloth as a pouch or a bottle to stack the layers and hang it from a tree. Fill the pouch or bottle with layers of different materials working from coarse to fine as you go your way down the container. Pour the water into the top end of the pouch or bottle and allow it to work its way down through the layers
If you consume untreated water, you run the risk of becoming infected with a water-borne disease, so it’s vital that you treat any water first. If you have the ability to start a fire, the most effective way of making water safe to drink is by boiling it from at least 10 minutes. However if you are unable to make a fire, there are several devices available that are capable of filtering and purifying water to make it safe for drinking.
These are specially designed units that filter the water and then purify it, by pumping the contaminated water through either micro filters, chemicals or a combination of both. Sized vary in these devices from small pumps able t purify 10 gallons to units capable of purifying large quantities of water.
These devices are incorporated within drinking bottles. The water is either allowed to flow naturally through the system via gravity, or is squeezed through by the operator. All bottles of this type typically employ: a filter to remove sediments and organic contaminants; a micron filter to remove protozoa; and a chemical that kills water-borne bacteria and viruses.
Compact emergency water filters, survival straws usually contain a filter system and employ either carbon or iodine resign systems to eliminate water-borne diseases and harmful chemicals. You need to get the water at the point where you can reach it with your straw. If you want to draw a supply of water to carry with you, you’ll have to draw water into your mouth and decant it into a container.
Larger units, that provide safe water to multiple people and that use the same technology, are now commercially available.
If you can’t boil water, or if you don’t have a water purification device, you’ll have to rely on non-mechanical methods. The concentration and contact time required for some of these methods is dictated by the quality and temperature of the water being treated.
Iodine (Liquid and Tables)
Iodine, which destroys bacteria, viruses and cysts, can be used to disinfect water effectively and conveniently. Its action is dependent on concentration, the water temperature, and the duration of the contact. A concentration of 8mgs per liter at 68 F will destroy pathogens if left for 10 minutes.
Chlorine based tablets will destroy most bacteria but are less effective for viruses and cysts. They are more effective when used in combination with phosphoric acid and will destroy both Giardiasis and Cryptosporidium.
Potassium permanganate can be bought at most pharmacies. Mix a few granules with your water until it turns light pink. Leave for at least 30 minutes before drinking
Adding unscented household bleach is the cheapest way to add chlorine to water. Be careful to just add one drop of leach per liter of water, two if the water is cloudy, and leave for at least 30 minutes before drinking. This method is not always effective against Giardiasis and Cryptosporidium.
Note: Before employing any commercial device for water treatment, you should do your own research to ensure you are using appropriate devices to achieve the necessary level of treatment.