Solar Water Disinfection
More Articles Related to WaterAccess to clean drinkable water is a top priorty for survival wherever you are. You can live without food for several weeks if need be, but surviving without water for more than a few days under any conditions will certainly endanger you physically and mentally.
Water is heavy and bulky and difficult to carry around, so often you must obtain most of your water from local sources. But there is a problem with this. In the field you should consider all sources of water suspect. Microorganisms in water, such as giardia, can make you very sick and even cause long term complications. The last thing you need when in a survival situation is ill health. You need a water treatment system to make water safe to drink.
Even cold, clear water can be riddled with disease organisms. I remember one incident in the White Mountains of New Hampshire. I came upon a crystal clear cold mountain stream from which a cool refreshing drink would have felt very good. This seemingly cleanest of water sources had a nasty surprise, for just upstream was a rotting moose carcass over which the entire water course flowed!
How to Make Water Safe to Drink
There are a number of common ways to make water safe to drink. These include:
- Boiling
- Chemical Disinfection
- Filtering
Portable water filters have been around for a number of years. Hikers and outdoorsmen frequently carry lightweight water filters that weigh little more than a pound or two that can process hundreds of gallons of water. Considering that water weighs about a pound per pint, carrying these water filters is a very efficient way to ensure plenty of clean potable water.
Chemically treating water is another way of making water safe to drink. One disadvantage of treating water with chemicals is that often they are potentially dangerous if used improperly and may not be readily available when you need them.
An age old method of making water safe to drink is to boil it. Boiling water to make it safe to drink has its problems. For one thing it requires an energy source. In developing countries the fuel source is often wood. Gathering enough firewood to boil water day after day can take a great deal of time and effort. In some areas of the world whole forests have been cut in order to boil water to make it safe to drink. Many people must walk for miles scavenging for this fuel.
All of these methods for making drinkable water out of contaminated water require special equipment or a plentiful source of fuel energy. What if you are short of fuel to boil water, had no readily available means to chemically disinfect drinking water, or lacked a water filtration system? What if large quantities of water must be decontaminated over a long period of time easily and efficiently? What can the survivor do when he finds himself with plenty of potentially contaminated water but no traditional readily available method to destroy disease causing organisms?
What if I told you there is a simple way to treat water and make it safe to drink wherever you are? Of all the ways to make water safe to drink, the method most simple and energy efficient can be very close at hand just about anywhere in the world.
Introducing Solar Water Disinfection.
What is SODIS?
Solar Water Disinfection, also known as SODIS, is a water treatment system using two readily available materials: sunlight and plastic PET bottles.
SODIS solves the problem of making water safe from microorganisms that cause water borne diseases simply by placing contaminated water into clear plastic bottles and exposing them to the sunlight, This makes SODIS an excellent tool in the survivors kit.
EAWAG (The Swiss Federal Institute for Environmental Science and Technology) and SANDEC (EAWAG's Department of Water and Sanitation in Developing Countries) conducted extensive laboratory and field tests to develop and test the Solar Water Disinfection Process (SODIS). These efforts again proved this simple low cost method of making water safe to drink has great potential for those without access to safe drinking water.
How to Use the Sun to Make Water Safe to Drink
The SODIS water treatment system is as follows:
1. Find a clean, transparent plastic PET bottle of up to three liters in volume.
2. Fill the plastic pet bottle about three quarters full with clear water, or water that has been filtered through sand, or whatever you have at hand.
3. Shake the bottle vigourously for twenty seconds in order to dissolve as much oxygen as possible into the water to be disinfected.
4. Fill the remainder of the plastic PET bottle and replace the cap.
5. Place the plastic bottle in direct sunlight for six to eight hours. Resting on a highly reflective surface such as metal, light colored rock, or tin foil will improve the process
6. If the weather is cloudy, the length of daylight short, or the water is murky with suspended particles, leave the bottle outdoors in the sun for two full days.
7. The water is now disinfected and drinkable with 99.9% of living organisms having been destroyed.
How SODIS works
Sunlight is treating the contaminated water through three synergistic radiation mechanisms.
* UV-A (wavelength 320-400nm) which react with oxygen dissolved in the water produces highly reactive forms of oxygen (oxygen free radicals and hydrogen peroxides) in the water. These reactive forms of oxygen kill the microorganisms.
* UV-A also interferes with the reproduction cycle of bacteria by damaging their DNA
* Infrared heating the water. If the water temperatures raises above 50 degrees celsius or 122 degrees F, the disinfection process is three times faster.
The combined effect of all three mechanisms is greater than that of each individual components.
Notes:
SODIS efficiency depends on the physical condition of the plastic bottles. Mechanical scratches and aging reduce the efficiency of SODIS. Heavily scratched or old bottles should be replaced.
Solar Water Disinfection Considerations
The SODIS water treatment method requires solar radiation and temperature to destroy microorganisms. Using the solar water disinfection method does not remove chemical contamination.
The SODIS system works best in areas between 35 degrees north latitude and 35 degrees south latitude. The water to be treated should be exposed to the full sun for six hours when the sky is bright. If cloud cover is more than fifty percent, expose the contaminated water for two full days before drinking. If the temperature of the water can reach at least 50 degrees Celsius (122 degrees Fahrenheit) the time required for the solar disinfection of water can be as little as one hour under ideal conditions.
Particles that are suspended in the contaminated water will shield microorganisms from the full impact of solar radiation, so it is important to make the water as clear as possible. Water filtering or allowing the suspended particles to settle out before using the SODIS water treatment system will aid greatly in the solar disinfection process.
Containers Used for Solar Water Disinfection
The type and shape of the container used for SODIS water treatment is important.
Plastic PET bottles, which are made of PolyEthylene Terephtalate are considered the best choice since they do not have as much UV stabilizer as compared to PVC bottles, which are made of PolyVinylChloride. Bottles that are scratched will not work as well as clear clean plastic.
Glass bottles can be used for Solar Water Disinfection but are not nearly as efficient as PET bottles. Window glass in not recommended as it does not transmit enough UV radiaton.
Another important consideration when using SODIS to disinfect water is the depth of water in the container. The thinner the container the better, especially if the water has suspended particles. It has been found that if the the depth of water inside the PET container is ten centimeters, or about four inches, and the water has a moderate amount of suspended particles, the amount of UV-A radiation from the sun that penetrates the full volume is reduced by half. This will therefore increase the amount of time needed to successfully implement the solar water disinfection process.
Using SODIS in a Survival Situation
It is a sad fact that discarded plastic bottles can be found just about everywhere in the world. Even the remotest beach or river valley often contains a variety of human cast offs, one of the most common of which are plastic bottles.
If you are going to be in an area for an extended time, collect as many plastic PET bottles as you can, fill them with the water to be treated and place them in direct sunlight as shown in the SODIS instructions above.
If you are short on clean uncontaminated water, try to go as long as possible, at least a day, before drinking the SODIS treated water. Keep the plastic water bottles exposed to the sun as long as you are using them to insure the water remains free of pathogens. If possible place the bottles on a metal or dark surface to take advantage of heat and speed up the SODIS process. Refill bottles as soon as they are emptied, being sure to remember which bottles contain water that has been treated the for the longest time and which have been most recently filled.
If you are traveling, try to rig your water filled containers outside your pack or on the roof of your vehicle in order to expose them to the sun and heat as much as possible. This will help to further treat the water and prohibit the growth of new pathogenic organisms.
SODIS
Solar Water Disinfection is a five star method of making water safe to drink. SODIS materials are readily available, is environmentally friendly, is easy to implement, and can easily be taught to others. This makes the SODIS method of water treatment an excellent tool of the survivor.
In many areas of the world the SODIS method of making water safe to drink is being used, and with great success.
Other UV Light Methods to Make Water Safe to Drink
Steripens take the UV light method a step further. A steripen is a handheld battery operated device that emits 90% UV light and disinfects your water in under a minute.
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I think this is a great idea, but i heard that the sun destroys or breaks down part of the plastic bottle and that the chemicals from the bottle leach into your drinking water. And have this bottle in direct sunlight i imagine that would happen. There are new bottles out made of out types of metal to stop the plastic leaching. So i was wondering how harmful it would be, and if you realized that? I guess its still better then nothing for you wont be taking in any bacteria, thats great but was just wondering about that.
Thanks for all the information!
Texas
The only problem with this is that the plastic will leach into the water in the sun. Glass may be breakable, but it doesn't leach anything into your water!
Survival Topics - Good point Lisa, some clear glass will also work well. Of late there has been concern over plastics and leaching of chemicals. However glass is heavy, more breakable, and may not always be available.
I love this survival website!! this will be coming in real handy in about 4 years.
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