Post by Keith. on Dec 2, 2017 14:02:19 GMT 10
Welcome Keith, I'm going to get into the industrial pollutants later on the discussion.
For these elimination is a long shot, however having charcoal can help to a certain extent if we try to replicate (as much as we can) the properties of the granular activted carbon filters and of the powedered compacted carbon filters produced industrially.
On this topic I would like to give our readers the basics on what both activated carbon and compacted carbon filters do and dont to, so that they can make a judgment call when needed in preparing their filtration set up.
The general confusion in the survival community is on the set up of the carbon filter and on the expectations of the performance. Powdered compacted carbon filters, which are not activated, are working on the principle of limited porosity and therefore can stop Giardia and Cryptosporidum cysts by virtue of their size.
However what in survival we see is that the "charcoal' (likely taken from the camp fire) used in the filters is not Powdered and surely is not Highly Compacted, it is not Activated as well because activation is an industrial process which cannot be replicated in the wilderness, so it fails both the purpose of stopping cysts and other industrial pollutants.
The pieces, small or large, of the camp fire charcoal normally used absorb ,to a certain extent, some particles because of their intrinsic porosity, however in the set ups you see normally e.g. uncompacted small to medium chunks, they are as good as a two or three layers of tightly woven cloth. As a matter of fact, using the camp fire charcoal for filtering slime and sediments, can cause what in coal filtering is called "channeling" which is, once the slime and sediments clog the pores, the water takes the path of less resistance and the filter doesnt perfom anymore. You can spot this in gravity filtration by a sudden appreciable increase in the flow of water.
Paolo
UV or ULTRAVIOLET LIGHT
UV or Ultra Violet light is extremely effective for water disinfection and other disinfection applications.
However on the market there is only one product that has some of the features that would make it suitable, albeit not ideal, for wilderness applications, bearing in mind that a malfunction might leave you in very dire straits.
The product is called SteriPEN®, it is an electrically supplied device powered by rechargeable batteries. By the very fact that it has to emit UV light it has a lamp, which is, well protected against accidental damages.
It is handy and comes with one set of spare batteries, a neoprene belt pouch and a plastic container which incorporate solar photovoltaic cells to be able to recharge the depleted batteries using the sun. It takes up to 3-4 days to reach a complete charge. It has also a standard charger that can be plugged into the electricity supply.
The pen is water proof and comes with a rubber anti-shock liner; the lamp unit is also protected by a transparent plastic tube and an additional removable plastic protection.
It is easy to use and it can sterilize up to a liter of water in as little as one minute and half, albeit the water container must have a large enough mouth to be able to submerge the lamp element completely as well as allowing some steering of the liquid. It can be used to disinfect as little as one glass of water in a matter of seconds.
One set of batteries is enough for several treatments and will last enough to guarantee that the depleted batteries could be recharged with the slower solar power option.
These are all the features. Having said that it is more suitable for occasional traveler and campers, however for those who like gadgets or cannot use other disinfection methods, this is a very efficient device that might have a place in anyone gear as back-up device (see picture at the end of the chapter).
SODIS (Solar Water Disinfection)
This system is quite intriguing. Personally I haven’t tried it yet in the field but I have taken some time to familiarize myself with it just to be able, if push comes to shove, to use it.
As the old saying goes in war ammunitions are never too many.
The extent of the effectiveness of the SODIS system has been the subject of extensive field testing in various developing countries and its efficacy and limitations, has been documented by thorough microbiological laboratory testing.
Data available clearly identify the extent and limitations of the method in neutralizing water borne pathogens (crawlies).
This in turn requires a bit of self study, however the advantage is that the information available allow us to make very informed decisions should we require putting it at work for water disinfection.
I would judge the system as efficient within its limitations, and certainly better than direct drinking of untreated water after a make shift filtration in a survival situation.
SODIS was developed by the Swiss Federal Institute for Environmental Sciences and Technology (EAWAG) in cooperation with EAWAG’ Department of Water Sanitation in Developing Countries (SANDEC). I encourage the readers to visit EAWAG website and familiarize with the information contained about the SODIS.
EAWAG is Swiss Government none profit organizations an aspect that rules out marketing related overrating of the system efficiency, an unethical aspect that plague even the survival industry even though human lives are potentially at stake.
The SODIS method is surprisingly simple, it utilizes spent transparent PET bottles (the majority of the current water and soda bottles) and the sunlight.
The whole system boils down to three easy steps:
-Filling spent transparent PET water or soda bottles ¾ of their capacity (most of them are 1.5 liters capacity) with the water to be treated and capping them,
-Shaking the bottle for 20-30 seconds in order to increase the water oxygenation,
-Leaving the bottles laying down on a clear reflective surface exposed to the sun light for a certain amount of time; 6 to 8 hours minimum in sunny weather, in poor weather up to 2 full days might be required.
That’s all there is to it.
The “variables” and “limitations” of the method are several, we will look at them.
The principles on which the method is based are scientifically sound and proven, this implies that the limitations of the methods are equally well defined.
Let’s look at the principles first. What does sunlight do?
Water borne pathogens (the crawlies), albeit not all of them, are susceptible to two effects of the sunlight:
-Some of the crawlies are vulnerable to the UV-A* radiations
-Some of the crawlies are vulnerable to heat which is the effect of solar infrared radiations
*UV-A is one of the bands of Ultra Violet light. Lights, visible or not to the human eye, are divided in categories on the basis of their wavelength (imagine the sea waves and the distance between the tops of two consecutive waives). Ultra Violet light, not visible to human, is subdivided into several subcategories of wavelength of which the “A” category is the one with the longer span. UV light stands in between the visible light to human eye and the X-Ray light.
Briefly, UV-A reacts with oxygen dissolved in the water producing what are called oxygen free radicals and hydrogen peroxides in the water. These two products kill the microorganisms. UV-A also interferes with the reproduction cycle of bacteria by damaging their DNA.
Infrared radiations, by heating the water, accelerate the above processes at temperatures at or above 50°C.
SODIS achieve a substantial reduction of the crawlies in the water but not the complete elimination (this has been corroborated by extensive laboratory tests which are still ongoing due to the complexity of the various crawlies reactions to the UV-A under a variety of environmental conditions).
However seen from the angle of providing reasonable water sanitation in large scale, the method is a simple, almost no cost alternative for the developing countries where mortality due water borne pathogens infections claims the life of thousands of people, amongst them, children which have reduced immune system efficiency.
*I call this the “mine field” probability game, if you have to walk through a mine field your chances of survival are much better if the density is 5 mines per square kilometer than if you have 300 of them. People in some developing countries have no other option but to walk mine field and in some survival circumstances, we might have to as well.
Let’s see how SODIS, under optimal conditions, performs. While we are going to talk about other crawlies later (Parasites, Bacteria and Viruses) we are going to mention them in illustrating the “crawlies killing” results of the SODIS system.
It has to be mentioned that according to international health standards, the accepted indicator for water quality is the presence of the so called Escherichia Coli (E. Coli), a bacteria thriving in presence of fecal contamination of water supplies typical of developing countries (but not only) and responsible for a good portion of the health problems experienced by the population.
SODIS application has resulted in the following results (UV-A induced reduction or inactivation):
Bacteria:
E. Coli (Gastro-Enteritis) 3-4 log reduction*
Vibrio Cholera (Cholera) 3-4 log reduction
Salmonella (Typhoid) 3-4 log reduction
Shigella (Dysentery) 3-4 log reduction
Viruses:
Rotavirus (Diarrhea, Dysentery) 3-4 log reduction
Polio Virus (Polio) inactivation results not known**
Hepatitis Virus (Hepatitis) reduction present but not quantified**
Protozoa:
Giardia L. (Giardiasis) 3-4 log reduction of the infectivity of the cysts
Cryptosporidium (cryptosporidiosis) 3-4 log reduction of the infectivity of the cysts
*Log (which stands for the mathematical logarithm) 3-4 is a conventional way of indicating the % of reduction of microorganisms in microbiology. For reference here are the % values related to various Log indication:
0.5 log = 68.4 % reduction/inactivation
1 log = 90%
2 log = 99%
3 log = 99.9%
4 log = 99.99%
5 log = 99.999%
So 3-4 log reduction or inactivation indicates that between 99.9% and 99.99% of the crawlies indicated with this number have been either killed or disabled. That’s pretty good on paper, however we must consider that mathematic doesn’t always translate in absolute safety on the ground.
The log reduction unit of measurement doesn’t show a variable that is the number of crawlies in the water.
Looking at the ubiquitous and tough Crypto (a friendly nickname of the Cryptosporidium) to pick one; suppose we have a log 3 reduction performance, the end result changes if we have 1,000,000 cysts or 1,000 cysts in our water.
At 1,000,000 cysts a log 3 (99.9%) result means we are left with 1,000 Cryptos roaming around.
At 1,000 cysts a log 3 result means we are left with 1 Cryptos roaming around.
So beware of the laboratory results, there is no way we can measure the Crypto or any other crawly number into the water and some of them don’t need too many of them to cause problems.
However having cautioned the readers against mathematic and statistics, I want to emphasize that, if nothing else is available the method is the best you can get with the little as possible.
Considering that most of us are vaccinated against Hepatitis and Polio and that, in the wilderness, the crawlies load (quantity) in the available water sources can be reasonably lower than in some villages in the middle of some developing countries by virtue of the lower population density (human and animals like cows, dogs, cats, etc. In the village everyone does everything, including defecating, in close proximity of water sources), SODIS is a good bet if push comes to shove.
Let’s look now at the parameters for applying this method.
Intensity of solar radiation.
The SODIS is most efficiently applied in regions comprised between latitudes 15°N and 35°N (South as well) due to the lower precipitations and therefore higher average solar radiation yearly (more than 3,000 hours/year of sunshine).
The next region is the one comprised between latitudes 15°N and 15°S, the equatorial region. Humidity and rain reduced the yearly radiation, however through scattered clouds about 2,500 hours/year of sunshine can be achieved).
Seasonal and daily variation of solar radiations.
The seasonal variation is responsible for the climate in the region; regions near the equator experience the least amount of variation throughout the year, northern latitudes experience more.
In very sunny days, 6-8 hours complete the treatment, provided other variables are respected (condition of the bottle and cloudiness of the water), in presence of a complete overcast sky (but no rain), 48 hours is likely the most appropriate time as the dose of solar radiations is reduced by 1/3rd .
Scattered clouds sky cover, still is sufficient for the treatment to be effective with a time in between those indicated above.
During rainy days the method is not effective. However if it rains, we can collect rain and drink that.
Temperature.
If the water temperature reaches 50°C or above, the treatment efficacy is greatly improved. However in the wilderness we don’t always have a thermometer, but we can help the temperature increase by construction a reflective surface on which to lay the bottles.
A piece of discarded undulated metal sheet cover, the roof of the car, anything shiny and metallic will do.
I carry always about a yard of aluminum foil, the one used for food wrapping, carefully folded, into my pack; it serves many purposed, in this case it makes for an excellent reflective surface if arranged in a V shape under the bottle.
Water turbidity.
If the water if turbid SODIS won’t work very well (radiations can’t go through effectively). Filter it or decant it with the known systems mentioned early on (I didn’t include flocculation since if we have ashes we should have had fire and we should have thought about water before).
The minimum turbidity level should be below 30 NTU (Nephelometric Turbidity Units). Since not everyone can measure NTU’s outside a laboratory a little trick is in order.
If you have a compass, the brass 18th century type we all carry, place the compass under the 3/4 filled bottle with the bottle standing on it in the shade. Look through the bottle opening and if you can see the compass’ needle with reasonable clarity the water turbidity should be around 30 NTU or less.
For those who need glasses, wear them, since as you know, without glasses we couldn’t see the compass even looking through a bottle of gin.
Conditions of the PET bottle.
The bottle should not be scratched or aged to the extent that their surface becomes almost none transparent. This will hamper the radiation passing through.
Another good aspect of PET is that above 65°C starts to deform visibly. If the bottle starts to assume funny shapes or starts to feel flimsy at the touch, it is a good indication that the temperature of the water and bottle has reached a level that makes the whole contraption work well. It will not melt, so don’t worry.
Depth of the water to be treated.
10 cm water level in the bottle is as much as we can go. Allow for this when filling the bottle (remember that the bottle must be laid down exposed to the sun, not left standing).
Water Oxygenation.
Remember to shake the bottle for 20-30 seconds to increase oxygenation. DO NOT shake it during the treatment.
What about other materials such as PVC or Glass?
PVC can be used, however both PVC and PET bottles contains a certain amount of additives amongst them UV stabilizers which increase the stability of the material and protect the content from oxidizing and UV radiation.
PET bottle have been found to have much less of this UV unfriendly matters.
Glass. The capability of UV radiations to pass through glass is determined by the amount of Iron Oxide used in the manufacturing process.
To provide a benchmark consider that a 2mm window glass allows close to zero UV radiations to pass. Pyrex glass used for cooking pans allows more UV to pass, however I do not normally carry a Pyrex pot in the wilderness, my wife won’t allow me……….
I beg our readers pardon for the apparent theoretical mark of this chapter, however the understanding to the variable of this little know method of water treatment is important for the correct application.
As I said, it is not 100% effective, however it is a good bet, if it is a sunny day and nothing else is available and sometimes, survival, comes down to a series of informed bets which, in a way or another, buy us time and the more time we buy the more chances we have to make it out.
Paolo
(To be continued…..)
For these elimination is a long shot, however having charcoal can help to a certain extent if we try to replicate (as much as we can) the properties of the granular activted carbon filters and of the powedered compacted carbon filters produced industrially.
On this topic I would like to give our readers the basics on what both activated carbon and compacted carbon filters do and dont to, so that they can make a judgment call when needed in preparing their filtration set up.
The general confusion in the survival community is on the set up of the carbon filter and on the expectations of the performance. Powdered compacted carbon filters, which are not activated, are working on the principle of limited porosity and therefore can stop Giardia and Cryptosporidum cysts by virtue of their size.
However what in survival we see is that the "charcoal' (likely taken from the camp fire) used in the filters is not Powdered and surely is not Highly Compacted, it is not Activated as well because activation is an industrial process which cannot be replicated in the wilderness, so it fails both the purpose of stopping cysts and other industrial pollutants.
The pieces, small or large, of the camp fire charcoal normally used absorb ,to a certain extent, some particles because of their intrinsic porosity, however in the set ups you see normally e.g. uncompacted small to medium chunks, they are as good as a two or three layers of tightly woven cloth. As a matter of fact, using the camp fire charcoal for filtering slime and sediments, can cause what in coal filtering is called "channeling" which is, once the slime and sediments clog the pores, the water takes the path of less resistance and the filter doesnt perfom anymore. You can spot this in gravity filtration by a sudden appreciable increase in the flow of water.
Paolo
UV or ULTRAVIOLET LIGHT
UV or Ultra Violet light is extremely effective for water disinfection and other disinfection applications.
However on the market there is only one product that has some of the features that would make it suitable, albeit not ideal, for wilderness applications, bearing in mind that a malfunction might leave you in very dire straits.
The product is called SteriPEN®, it is an electrically supplied device powered by rechargeable batteries. By the very fact that it has to emit UV light it has a lamp, which is, well protected against accidental damages.
It is handy and comes with one set of spare batteries, a neoprene belt pouch and a plastic container which incorporate solar photovoltaic cells to be able to recharge the depleted batteries using the sun. It takes up to 3-4 days to reach a complete charge. It has also a standard charger that can be plugged into the electricity supply.
The pen is water proof and comes with a rubber anti-shock liner; the lamp unit is also protected by a transparent plastic tube and an additional removable plastic protection.
It is easy to use and it can sterilize up to a liter of water in as little as one minute and half, albeit the water container must have a large enough mouth to be able to submerge the lamp element completely as well as allowing some steering of the liquid. It can be used to disinfect as little as one glass of water in a matter of seconds.
One set of batteries is enough for several treatments and will last enough to guarantee that the depleted batteries could be recharged with the slower solar power option.
These are all the features. Having said that it is more suitable for occasional traveler and campers, however for those who like gadgets or cannot use other disinfection methods, this is a very efficient device that might have a place in anyone gear as back-up device (see picture at the end of the chapter).
SODIS (Solar Water Disinfection)
This system is quite intriguing. Personally I haven’t tried it yet in the field but I have taken some time to familiarize myself with it just to be able, if push comes to shove, to use it.
As the old saying goes in war ammunitions are never too many.
The extent of the effectiveness of the SODIS system has been the subject of extensive field testing in various developing countries and its efficacy and limitations, has been documented by thorough microbiological laboratory testing.
Data available clearly identify the extent and limitations of the method in neutralizing water borne pathogens (crawlies).
This in turn requires a bit of self study, however the advantage is that the information available allow us to make very informed decisions should we require putting it at work for water disinfection.
I would judge the system as efficient within its limitations, and certainly better than direct drinking of untreated water after a make shift filtration in a survival situation.
SODIS was developed by the Swiss Federal Institute for Environmental Sciences and Technology (EAWAG) in cooperation with EAWAG’ Department of Water Sanitation in Developing Countries (SANDEC). I encourage the readers to visit EAWAG website and familiarize with the information contained about the SODIS.
EAWAG is Swiss Government none profit organizations an aspect that rules out marketing related overrating of the system efficiency, an unethical aspect that plague even the survival industry even though human lives are potentially at stake.
The SODIS method is surprisingly simple, it utilizes spent transparent PET bottles (the majority of the current water and soda bottles) and the sunlight.
The whole system boils down to three easy steps:
-Filling spent transparent PET water or soda bottles ¾ of their capacity (most of them are 1.5 liters capacity) with the water to be treated and capping them,
-Shaking the bottle for 20-30 seconds in order to increase the water oxygenation,
-Leaving the bottles laying down on a clear reflective surface exposed to the sun light for a certain amount of time; 6 to 8 hours minimum in sunny weather, in poor weather up to 2 full days might be required.
That’s all there is to it.
The “variables” and “limitations” of the method are several, we will look at them.
The principles on which the method is based are scientifically sound and proven, this implies that the limitations of the methods are equally well defined.
Let’s look at the principles first. What does sunlight do?
Water borne pathogens (the crawlies), albeit not all of them, are susceptible to two effects of the sunlight:
-Some of the crawlies are vulnerable to the UV-A* radiations
-Some of the crawlies are vulnerable to heat which is the effect of solar infrared radiations
*UV-A is one of the bands of Ultra Violet light. Lights, visible or not to the human eye, are divided in categories on the basis of their wavelength (imagine the sea waves and the distance between the tops of two consecutive waives). Ultra Violet light, not visible to human, is subdivided into several subcategories of wavelength of which the “A” category is the one with the longer span. UV light stands in between the visible light to human eye and the X-Ray light.
Briefly, UV-A reacts with oxygen dissolved in the water producing what are called oxygen free radicals and hydrogen peroxides in the water. These two products kill the microorganisms. UV-A also interferes with the reproduction cycle of bacteria by damaging their DNA.
Infrared radiations, by heating the water, accelerate the above processes at temperatures at or above 50°C.
SODIS achieve a substantial reduction of the crawlies in the water but not the complete elimination (this has been corroborated by extensive laboratory tests which are still ongoing due to the complexity of the various crawlies reactions to the UV-A under a variety of environmental conditions).
However seen from the angle of providing reasonable water sanitation in large scale, the method is a simple, almost no cost alternative for the developing countries where mortality due water borne pathogens infections claims the life of thousands of people, amongst them, children which have reduced immune system efficiency.
*I call this the “mine field” probability game, if you have to walk through a mine field your chances of survival are much better if the density is 5 mines per square kilometer than if you have 300 of them. People in some developing countries have no other option but to walk mine field and in some survival circumstances, we might have to as well.
Let’s see how SODIS, under optimal conditions, performs. While we are going to talk about other crawlies later (Parasites, Bacteria and Viruses) we are going to mention them in illustrating the “crawlies killing” results of the SODIS system.
It has to be mentioned that according to international health standards, the accepted indicator for water quality is the presence of the so called Escherichia Coli (E. Coli), a bacteria thriving in presence of fecal contamination of water supplies typical of developing countries (but not only) and responsible for a good portion of the health problems experienced by the population.
SODIS application has resulted in the following results (UV-A induced reduction or inactivation):
Bacteria:
E. Coli (Gastro-Enteritis) 3-4 log reduction*
Vibrio Cholera (Cholera) 3-4 log reduction
Salmonella (Typhoid) 3-4 log reduction
Shigella (Dysentery) 3-4 log reduction
Viruses:
Rotavirus (Diarrhea, Dysentery) 3-4 log reduction
Polio Virus (Polio) inactivation results not known**
Hepatitis Virus (Hepatitis) reduction present but not quantified**
Protozoa:
Giardia L. (Giardiasis) 3-4 log reduction of the infectivity of the cysts
Cryptosporidium (cryptosporidiosis) 3-4 log reduction of the infectivity of the cysts
*Log (which stands for the mathematical logarithm) 3-4 is a conventional way of indicating the % of reduction of microorganisms in microbiology. For reference here are the % values related to various Log indication:
0.5 log = 68.4 % reduction/inactivation
1 log = 90%
2 log = 99%
3 log = 99.9%
4 log = 99.99%
5 log = 99.999%
So 3-4 log reduction or inactivation indicates that between 99.9% and 99.99% of the crawlies indicated with this number have been either killed or disabled. That’s pretty good on paper, however we must consider that mathematic doesn’t always translate in absolute safety on the ground.
The log reduction unit of measurement doesn’t show a variable that is the number of crawlies in the water.
Looking at the ubiquitous and tough Crypto (a friendly nickname of the Cryptosporidium) to pick one; suppose we have a log 3 reduction performance, the end result changes if we have 1,000,000 cysts or 1,000 cysts in our water.
At 1,000,000 cysts a log 3 (99.9%) result means we are left with 1,000 Cryptos roaming around.
At 1,000 cysts a log 3 result means we are left with 1 Cryptos roaming around.
So beware of the laboratory results, there is no way we can measure the Crypto or any other crawly number into the water and some of them don’t need too many of them to cause problems.
However having cautioned the readers against mathematic and statistics, I want to emphasize that, if nothing else is available the method is the best you can get with the little as possible.
Considering that most of us are vaccinated against Hepatitis and Polio and that, in the wilderness, the crawlies load (quantity) in the available water sources can be reasonably lower than in some villages in the middle of some developing countries by virtue of the lower population density (human and animals like cows, dogs, cats, etc. In the village everyone does everything, including defecating, in close proximity of water sources), SODIS is a good bet if push comes to shove.
Let’s look now at the parameters for applying this method.
Intensity of solar radiation.
The SODIS is most efficiently applied in regions comprised between latitudes 15°N and 35°N (South as well) due to the lower precipitations and therefore higher average solar radiation yearly (more than 3,000 hours/year of sunshine).
The next region is the one comprised between latitudes 15°N and 15°S, the equatorial region. Humidity and rain reduced the yearly radiation, however through scattered clouds about 2,500 hours/year of sunshine can be achieved).
Seasonal and daily variation of solar radiations.
The seasonal variation is responsible for the climate in the region; regions near the equator experience the least amount of variation throughout the year, northern latitudes experience more.
In very sunny days, 6-8 hours complete the treatment, provided other variables are respected (condition of the bottle and cloudiness of the water), in presence of a complete overcast sky (but no rain), 48 hours is likely the most appropriate time as the dose of solar radiations is reduced by 1/3rd .
Scattered clouds sky cover, still is sufficient for the treatment to be effective with a time in between those indicated above.
During rainy days the method is not effective. However if it rains, we can collect rain and drink that.
Temperature.
If the water temperature reaches 50°C or above, the treatment efficacy is greatly improved. However in the wilderness we don’t always have a thermometer, but we can help the temperature increase by construction a reflective surface on which to lay the bottles.
A piece of discarded undulated metal sheet cover, the roof of the car, anything shiny and metallic will do.
I carry always about a yard of aluminum foil, the one used for food wrapping, carefully folded, into my pack; it serves many purposed, in this case it makes for an excellent reflective surface if arranged in a V shape under the bottle.
Water turbidity.
If the water if turbid SODIS won’t work very well (radiations can’t go through effectively). Filter it or decant it with the known systems mentioned early on (I didn’t include flocculation since if we have ashes we should have had fire and we should have thought about water before).
The minimum turbidity level should be below 30 NTU (Nephelometric Turbidity Units). Since not everyone can measure NTU’s outside a laboratory a little trick is in order.
If you have a compass, the brass 18th century type we all carry, place the compass under the 3/4 filled bottle with the bottle standing on it in the shade. Look through the bottle opening and if you can see the compass’ needle with reasonable clarity the water turbidity should be around 30 NTU or less.
For those who need glasses, wear them, since as you know, without glasses we couldn’t see the compass even looking through a bottle of gin.
Conditions of the PET bottle.
The bottle should not be scratched or aged to the extent that their surface becomes almost none transparent. This will hamper the radiation passing through.
Another good aspect of PET is that above 65°C starts to deform visibly. If the bottle starts to assume funny shapes or starts to feel flimsy at the touch, it is a good indication that the temperature of the water and bottle has reached a level that makes the whole contraption work well. It will not melt, so don’t worry.
Depth of the water to be treated.
10 cm water level in the bottle is as much as we can go. Allow for this when filling the bottle (remember that the bottle must be laid down exposed to the sun, not left standing).
Water Oxygenation.
Remember to shake the bottle for 20-30 seconds to increase oxygenation. DO NOT shake it during the treatment.
What about other materials such as PVC or Glass?
PVC can be used, however both PVC and PET bottles contains a certain amount of additives amongst them UV stabilizers which increase the stability of the material and protect the content from oxidizing and UV radiation.
PET bottle have been found to have much less of this UV unfriendly matters.
Glass. The capability of UV radiations to pass through glass is determined by the amount of Iron Oxide used in the manufacturing process.
To provide a benchmark consider that a 2mm window glass allows close to zero UV radiations to pass. Pyrex glass used for cooking pans allows more UV to pass, however I do not normally carry a Pyrex pot in the wilderness, my wife won’t allow me……….
I beg our readers pardon for the apparent theoretical mark of this chapter, however the understanding to the variable of this little know method of water treatment is important for the correct application.
As I said, it is not 100% effective, however it is a good bet, if it is a sunny day and nothing else is available and sometimes, survival, comes down to a series of informed bets which, in a way or another, buy us time and the more time we buy the more chances we have to make it out.
Paolo
(To be continued…..)