purified water (via exposure to the sun) (Water)greenspun.com : LUSENET : Countryside : One Thread
My girl friend told me that she heard on the CBC Canadian radio, that after all these years of trying to find clean water for people in third world countries, they have found out that by filling plastic pop bottles and leaving them in the sun for a certain amount of time purifies drinking water. Has anyone heard of this. It seems to simple to believe. Would this simple solution remove all harmful bacteria?
-- debbie mulder (firstname.lastname@example.org), May 04, 2001
Public health officials recomment that suspect drinking water be brought to a rolling boil, 212F, for about 5 min. before consumption. But milk, fruit juices, etc. are pasteurized at about 170F for a very short time to kill pathogenic bacteria and are then deemed OK for consumption by the public. Personally, I don't know why this discrepancy exists. I do understand that virtually all pathogenic bacteria are very sensitive to temperature, although I am not sure about their spore stages. Maybe some folks have decided that pasteurization temperatures are now OK for drinking water. I have not heard of this, however.
It is possible that water in plastic bottles under the tropical sun could reach 170F in a few hours, depending on the exact conditions, e.g. a black background, air circulation, etc. But there are other pathogens, e.g. protozoa like Cryptosporidium and Girardia, that are not easily killed at pasteurization temperatures. However, they are generally fairly large and most can be removed with a 5 micron filter, which is fairly coarse relative to bacterial filters.
To me, the bottom line is that solar radiation in the USA is a far cry from the equatorial sun of most third-world countries and I would think it unlikely that water in plastic bottles could reach pasteurization temperatures. The water certainly cannot reach boiling temperatures in soda bottles because the plastic melts long before 212F.
I can see no way for some magic combination of plastic and sunlight that would kill pathogens of any sort, other than temperature. In other words, my opinion is: don't do it unless you know exactly what you are doing. I think it's a good idea, though and is something I will try to remember for an emergency.
-- Marty Boraas (email@example.com), May 04, 2001.
However a solar cooker will get the water hot enough to purify....Kirk
-- Kirk Davis (firstname.lastname@example.org), May 05, 2001.
Folks, I don't think the idea is to pasteurize the water. I suspect (and it is only a suspicion) that the idea is that the sun would purify the water by subjecting the pathogens to ultraviolet light. After all, ultraviolet light is a currently used method for purifying water.
The reason plastic pop bottles are mentioned is probably due to the fact that a large percentage of ultraviolet light is filtered out by passing through glass. At least that's my recollection, from years ago.
In fact, I remember reading that, not too long ago, ultraviolet water purifyers came way down in price by being able to use "tygon tubing" to pass the water right next to the ultraviolet bulb. In the past, since glass tubes were not suitable for this, QUARTZ tubes had been used, which was a big part of the system's cost.
I'd recommend more research into this before relying on it to cure your water ills. For instance, how long does it take to kill which type of pathogens? Are some pathogens able to survive the exposure to ultraviolet light? Etc.
By the way, ultravioltet purifiers have never been good at treating turbid water. The light has to be able to easily penetrate the water for it to work.
-- jumpoff joe (email@example.com), May 05, 2001.
Dang, I wrote a fairly long note, and it disappeared. So I'll just give y'all a url, which is very good, and pretty comprehensive:
the pop bottle purification does appear to be very effective against bacteria, and there are data to back that up. There is also speculation, and calls for further testing, in regards to other pathogens, e.g. viruses, protazoa, etc.
-- jumpoff joe (firstname.lastname@example.org), May 05, 2001.
Please be very careful with this, and check it out thoroughly. I'm assuming you're Canadian. Maybe check with Health Canada, or even CBC Radio archives? Given the current problem in North Battleford, Sask., and last year's problem in Walkerton, Ont., check, check, check. Last summer I came down with the Giardia parasite (otherwise known as Beaver Fever). I suspect it was from a coffee I picked up along the Trans Canada Highway. It was devastating. I came down with it the end of June, and wasn't back to normal until the end of September. I lost more than 20 of my 116 pounds. I couldn't even care for my kids. Please be very careful.
-- Rheba in Ontario (email@example.com), May 05, 2001.
Even if its possible to kill bacteria, etc, I personally don't think plastic and heat are a good combination for food/drink containers. Many plastics leach what very likely are carcinogenic chemicals into the contents.
-- Earthmama (firstname.lastname@example.org), May 06, 2001.
I agree that plastic and heat aren't a healthy combination. The beauty of this purification system, though, is that it doesn't depend on heat.
-- jumpoff joe (email@example.com), May 07, 2001.
Sunlight will clear up most bacterial and fungal stuff in water, but will NOT remove several chemicals... among them cyanide and arsenic.
Also, if there is a very large percentage of animal waste in the water, it will not neutralize it all.
For water that is relatively pure to start with, yes... For water which may be contaminated near mines (especially) or animal dens, or sewage, no.
-- Sue Diederich (firstname.lastname@example.org), May 07, 2001.
I did a google search for "solar water purification" and came up with lots of info. The "lie it in bottles in the sun" does rely on pasteurisation, and does reduce rather than eliminate microorganisms, as anyone who's found an old bottle of pasteurised milk in the back of the fridge will know. Things like giardia are often in an encysted form, and hence protected to some extent, too.
Sue is right about other things in water - particularly arsenic. One of the big disasters in the world at the moment is that the World Health Organisation is in the process of poisoning tens of millions of people in Bangla Desh. They tried to give them unpolluted water by sinking village wells all over the place, but it turns out those wells are heavily contaminated with arsenic, and the people are so heavily committed to their use now that they can't go back to the old ways. Pictures of people suffering arsenic poisoning are NOT pretty. That search I did turned up a lot of references to solar distillation as well, and distillation will give pure water, but it costs a lot.
-- Don Armstrong (email@example.com), May 08, 2001.
Don, I don't think you did quite enough searching at Google.com. Yes, you can pasteurize water with solar energy, but I believe that this is not the method Debbie's referring to. Please read my post, above.
And Sue, and Don, are right about this method not purifying some dissolved minerals. So it is wise to find out if this is a problem in your water supply (President Select Bush tells us that Arsenic is not that big a deal. Thanks, Dubyuh)
On the other hand, hardly ANY water purification systems commonly used by homesteaders will remove these substances. Here's a list of the water purification systems that WILL NOT:
Chlorination Ozonation Filtration Iodine Carbon filtration Ultraviolet light Boiling
That's all I can think of , offhand, but the point is, dissolved minerals are a whole nuther beast than biological contaminants, which I believe is the question asked by Debbie in the first place.
-- jumpoff joe (firstname.lastname@example.org), May 08, 2001.
I think the only real purification is done by distillation, that way minerals such as arsenic will not be in the water. What about condensation, is there a way to collect water by condensation?
-- Janet (email@example.com), May 11, 2001.
Janet, if you have a problem with arsenic, don't worry about it. G dubya says it's fine.
Seriously, get the water tested, and if there's arenic, or other baddies, in unhealthy concentrations, consider buyiing bottled water to drink and cook with, or getting water for these purposes from a friend.
I have been told that the "normal" minerals in water are good for us, so I'm not so sure about distilled water for normal fare..
I could be wrong, though. Anyone else heard anything about this? I did hear that distlled water helps make great coffee.
-- jumpoff joe (firstname.lastname@example.org), May 11, 2001.