Posts Tagged ‘SODIS’

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Water Filtration

Often when you find water, it can often be cloudy murky and full of debris like leaves, dirt, insects and many other foreign bodies. This water will not be suitable to drink until it has been filtered to remove impurities.

Filtration should not be confused with sterilization. Whilst filtration will clear the water of debris, make it clearer and often make it taste and smell better, it will not remove bacteria so unless you are highly confident that the water is fresh, it always pays to sterilize it with water sterilization tablets, or by boiling or distilling it.

Fortunately there are many ways of filtering out the yucky bits with things which are readily available in the wild. The basic idea is to remove debris of all sizes by passing the water through different sized filters. Sand, Dried Grass, Pebbles and Charcoal all make excellent filtration material. Combine some of these in layers (smallest to largest) in a sock or your pants leg/shirt sleeve tied at the end and you’ll be good to go. Pass the water through the layers of filter material, catching the clean water as it comes out the bottom. It often pays, to run a couple of cups through the filter just to remove any fine dust or charcoal powder which may initially come through.

The type of filter that you will make will depend on the resources you have available at the time and how you intend to use the filter. There are several variations of the basic filter as mentioned above and then there are also some man made solutions which you may be fortunate enough to have with you. The following techniques listed are just some ideas but with a little ingenuity and resourcefulness, your options are almost limitless.

Charcoal is an extremely good filtration material as the carbon in it attracts impurities and improves the taste and smell of water. Always make sure that, if you light a fire or come across charcoal on your journey, that you take some with you. Aside from filtration, Charcoal has many other uses for the survivor. It will take a spark relatively easily and produce an ember and it is also useful to rub on your face for camouflage or under your eyes in the desert to reduce glare off your cheeks.

Gypsy Filter

A great method for filtering water from a pool if you don’t have the means to boil it is by digging a hole beside a pool of water (1ft/ 30-40cm away and deeper than the water level in the pool) and creating a well.

Let this sit for a while and the water will filter through the dirt and sand, filling the well.

This water will initially be murky so scoop that water out and let it fill up again. This time the water will be clearer and good to drink.

Charcoal Straw Filter

Sometimes the only water available is in a crack or pool which is too shallow to fill a cup. This is when a filter straw comes in handy.
You must find something long and hollow like a straw. This maybe a piece of frame from a backpack or a length of hollow stalk from a dried plant or Reid. Stuff this with a wad of dried grass and push it down with a stick. place crushed charcoal in the straw next followed by sand. Finally place another wad of dried grass in the end and pack it down (not too firm but firm enough to hold the filtration material in place). You should now be able to drink the water directly through the straw.

Commercial Water Filter Straws

These nifty little devices can be purchased from most camping and fishing stores and are a nice edition to your survival pouch. Use them to drink right from the water source. They will filter the water and also kill about 95% of any bacteria. They can be used for about a week before they need to be discarded.

Bamboo Filter

Cutting a section of thick bamboo so that it is hollow at both ends then packing one end with a wad of grass and then filling it to 3/4 with sand will make an excellent filter.

Water Sterilization Tablets

These can be purchases from most camping and fishing stores and are a handy addition to your survival tin. The manufacturers instructions on the packet should be followed.

UV Water Sterilization Pen

The handy devices are relatively new on the market, and are a really handy piece of kit to carry on your adventures. Retailing at around $260USD, they work by you shining the UV light into the water. UV light scrambles the DNA of nasty disease-causing bacteria, viruses and parasitic protozoa causing it to become inactive. At a relative lightweight 110g (3.8oz) incl. batteries they will disinfect 500ml (1pt) of clear water with just under a 50 second burst. These can also double as a torch and can be purchased from high-end outdoor adventure stores.

Disinfecting Water Using the Sun

The SODIS (Solar Disinfection) Method has been developed for developing countries as a low cost method for disinfecting water and eliminating diarrhea causing bacteria making it fit to drink. This method uses the sun’s UV rays to break down the bacteria and is endorsed by the World Health Organization. This technique involves filling clear PET plastic bottles with the suspect water and placing the cap firmly before laying the bottles out in the open, exposed to the sun, for the period of time specified below, depending on the weather conditions.

Suggested Treatment Schedule
Weather Conditions                        Minimum Treatment Duration
Sunny………………………………. 6 hours
50% cloudy………………………… 6 hours
50-100% cloudy…………………… 2 days
Continuous rainfall………………… Use rainwater!

This process can be hastened by laying a piece of corrugated iron against something so that is on a 45deg angle, facing the sun, and leaning the bottles against it so that they get maximum exposure to the suns rays.

If the water is very cloudy to begin with, it will need to be filtered prior to bottling. Once treated, the water can be stored in the bottle and consumed straight from the bottle.

SODIS Diagram
Image Courtesy of Wikipedia

Adapting the SODIS method for Survival

This very effective technique could easily be adapted to both wilderness and urban survival situations and could be used by soldiers, troopers, scouts etc who are in an open top observation post (OP) and low on supplies. The advantage of using this method in a tactical/combat situation is that the is no need to alter the natural surroundings and no need for a fire; both of which would likely compromise your position and potentially your life. If used in this situation though, it is important that the containers are placed in a position low out of sight, perhaps even below ground level, so as not to produce shine or glare which could also give your position away.

When adapting this technique to a survival situation, the general method stays the same but the materials that you use may differ depending on what is available to you at the time. Plastic PET bottles may be substituted for glass or clear plastic bag, tied closed, and they may be laid against a rock or simply flat on the ground. Unfortunately for the planet, in this day and age, there are not too many places left on earth where you will not find some form of litter laying around. Fortunately, as a survivor, you can often find useful things amongst litter such as plastic PET bottles or even glass this will be even more prevalent along coastal areas. Of course you may need to improvise a cap/lid and you could make a plug this with a wad of fabric or leaves and then seal it over with mud or wild bees wax.
Clear bottles with a minimal amount of scratches work best.

This technique is very effective as:

  • The yield is only limited by the size/amount of bottles that you have.
  • The process doesn’t take too long
  • The method can be carried out in a discreet, clandestine manner
  • The method is effective in all weather conditions
  • Requires low/no physical exertion
Water which comes from pools where there is no green vegetation growing, has bones or carcasses in or around it or has chalky rings around it should still be avoided as it is likely to have chemical contaminants.
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