Comments to: Low-tech Solar Water Purification: It works

Posted on March 25, 2006, 3:40 pm
by ronald kirk

very, very good and very interesting.This is a MUST for thousands of our rural people. I mean the sun sterilisation of drinking water.


Posted on March 27, 2006, 10:22 pm
by Donna Russell

How does the process of solar heating of the drinking water effect the leaching of the toxic chemicals of the plastic bottles into the water?

Granted, ill effects or death from the toxic chemical contamination will take much longer to manifest than the immediate illnesses and deaths produced from drinking water carrying diseases and parasites, but is there any developments looking at eliminating this problem?


Posted on March 28, 2006, 10:33 am
by Sepp


I have not heard anything about concerns over the chemicals that at times leak from the plastic bottles. Obviously, for these villagers the immediate gain of absence of infective water-born diseases is of greater concern than a largely theoretical and long-term contamination of the water with phtalates and other chemical goodies.

They could use clear glass bottles, if available, but in a poor rural environment, you use what you have - and that's plastic soft-drink or water bottles.


Posted on May 30, 2006, 11:12 am
by vish

This also brings up a related question of inert materials for water containers.

You've pointed out glass as a prime example. I was wondering if there is a list of metals/metallic compounds which provide for the "inert" property? And will these metals be effective for the above mentioned solar heating?

I asked, because glass can be fragile and a suitable replacement would be best for backpackers or campers in the wilderness.


Posted on September 4, 2006, 4:40 am
by Robert

This question was looked at in a well designed study, taking plastic bottles from third world countries. The results may be found at: (link no longer active - Sepp)

Basically, they found that the level of "plasticizers" were no higher than water not exposed to plastic.

Visit the home page

for more information.


Posted on March 1, 2008, 11:49 am
by Jacquie Hale

I've just returned from Tanzania and was investigating using discarded water bottles as building materials. I got very excited when I ready your article. I'm wondering if you have more information about the possibility of toxic ingredients leaching from the plastic when the bottles are heated by the sun or subjected to the UV rays.

Please contact me if there is a program already in place because I want to see that one does get started in as many African communities as I can.

THanks you,
Jacuqie Hale


Posted on March 1, 2008, 1:19 pm
by Sepp

Hi Jacquie,

thank you for your comment on the article regarding solar water purification.

About the possibility of toxins leaching, I saw an article two months ago that said no. Couldn't find that exact one again, but searching today I find:

Almost all soft drink and water bottles are made out of polyethylene terephthalate (PET), which is a polyester that, unlike vinyl, doesn’t require the use of orthophthalates for flexibilty. PET has not been found to be toxic (it’s biologically inert if ingested) and is not an endocrine disruptor.

(from: )

Whether there is a program in place, I wouldn't know. But whatever you find already exists, or whatever you manage to get going yourself, if you could post some information as a comment here, it would help others in the future...


Posted on July 29, 2008, 4:13 pm
by Eric

How does the recent evidence of plastic bottle "out-gassing" affect how the solar purification can be implemented?

Out-gassing, in this case, refers to the leaching of harmful (carcinogenic) substances from a plastic water bottle into its contents. It occurs when the bottle is exposed to heat, such as that of a car in a parking lot, or a tar roof in Africa. The affects of drinking such water are long-term.

I'm no expert, and this article was published before the more recent evidence of out-gassing of which I am aware. Of course, having safe drinking water trumps most concerns, especially those of the long-term.

Perhaps the use of glass, or any non-plastic bottles, as with the Chinese farmer above, would be a simple solution.


Posted on August 10, 2008, 5:41 am
by Andrew K Fletcher

Great article. Did a search to advise someone on Youtube about the use of these bottles and clicked on the first link (Auto Pilot) Was delighted to find I was viewing Your Pages again Sepp. :)

This use of Solar Disinfection has great potential throught areas that have little in the way of safe drinking water. I first read about this being used in Africa many years ago, adopted by people have no option but to drink dirty water if there is no safe method of decontaminating it. These bottles are ingenious and we thrown them away in the West without giving them a second thought.

Andrew K Fletcher


Posted on August 27, 2008, 8:35 am
by threenorns

hi - i can see that working in countries close to the equator but how would it translate to higher or lower latitudes where more UV is blocked by passing through a thicker atmosphere?


Posted on September 19, 2008, 12:00 pm
by kanza

hey this is very good and quite authenticccc but i need some more information so please help!!!!!


Posted on September 24, 2008, 4:57 pm
by Sepp

I believe that the plastic used for water and soft drink bottles (which is what's being used here) is not made with bisphenol A or BPA, which is supposed to be the toxic compound.

Unless you have different information, this should not be a great worry.


Posted on April 29, 2009, 12:12 pm
by Joann

1. How would this Solar Disinfection method work in a place such as India that has monsoon seasons?

2. Would you recommend an alternative and easily maintained water purification system that could supplement the use of plastic bottles in the Solar Disinfection method?

3. I'm looking for a system that would purify water for a community of a few hundred people. I've found a link to the PotPaz site lists commencial vendors. Any recommendation for a vendor?


Posted on April 29, 2009, 4:32 pm
by Sepp

I would think that during monsoon, it is possible to catch rainwater and drink it.

If you have a few hundred people, you should probably look around for something more sturdy than disinfection with the use of plastic bottles.

That PotPaz ceramic filter looks good. I have no experience with this however to recommend a vendor.


Posted on June 9, 2009, 2:51 am
by viny

its really wierd what people have to do to get clean drinking water. and i wish this website was a bit more helpful i cant find what i need anywhere.

- - -

Reply by Sepp @viny,

and what is it you are looking for?


Posted on November 5, 2009, 1:03 pm
by hadji

Hello, thank you very much for this article. It is very interesting as we are always looking for ways to improve the drinking water of rural communities in Africa.

The quality of water is directly related to the health of local populations and most of the water sources are contaminated so this method if efficient could be absolutely revolutionary.

We will test it and go from there.



Posted on November 8, 2009, 3:55 pm
by Pam Smith

GREAT article...I am on my way to Nepal to work in a small orphanage right out of kathmandu..the water is a BIG issue with the children getting sick all the time. Can I take BLACK plastic and use this instead of black painted glass?
It would be awesome to build this. Would one of those thermometers made of wax be good to know when the temperature is good?

thank you


Posted on November 8, 2009, 4:51 pm
by Sepp

go ahead and experiment, Pam.

I would think black plastic is fine instead of painted glass. Try it out.

Wax thermometers? never heard of them, but I suppose you'll be able to find a normal thermometer there as well. Just don't break it ;)


Posted on March 21, 2010, 11:56 am
by manjesh gurubele

hi...its a great idea to purify water with saving energy, sir i m manjesh the student of diploma chemical engg. from india (m.p.) and i want to do this experiment as my colleg project, may i do it? and please give me advise as soon as that how can i do it. i hope u help me about this. thanks


Posted on March 22, 2010, 9:30 am
by Sepp

hi ... no need to ask. Just do your experiment and write up what you find.

I would be happy if you could tell us about your results, when you are finished.


Posted on May 24, 2010, 10:42 pm
by Jonathan Lowe

I think it is important to note that it is the ULTRAVIOLET RAYS not THERMAL HEAT destroying the pathogens. Using painted glass or anything which blocks the light rays from penetrating the water would nearly negate the sterilzation technique.


Posted on February 5, 2011, 5:18 am
by suriya

good and very interesting


Posted on October 18, 2011, 9:41 pm
by Justino B. Cabarles, Jr.

Wonderful. We can use this SODIS in the community we are helping in Masbate here in the Philippines. How I wish there is also a similar way of converting salt water to tap water.


Posted on June 8, 2012, 3:41 am
by chinna

it is nice
let i want know total working principle

Sepp's answer:
The principle is simple. The Sun has ultraviolet rays, which kill germs. When the water stays in the sun for a day, the germs are killed and the water is safer to drink.


Posted on September 20, 2012, 9:35 pm
by honey

thank you for the data


Posted on March 4, 2013, 11:00 am
by Sepp for subhas mohapatra

Subhas Mohapatra comments by email:

Dear Sepp

the solar water purification method described by you is innovative. I have been using it in rural India for nearly a decade. However, in rural India people have thatched houses and can not get black roof.

I have solved this problem through "mini-greenhouse" technology. All one needs to do is:

a) Place 4 rocks, one in each corner.

b) place the water bottles on a piece of black plastic film which is laid on the ground within the 4 rocks making sure that the rocks are at least 6" tall. If rocks are not available, earth can be piled high to represent the rock.

c) A clear plastic film is placed above the bottles such that there will be at least 6" clearance between the plastic film and the bottles underneath.

d) Stretch the plastic film in all directions over the rocks/earth mounds and then lay the edges of the clear plastic film such that it is buried under the ground and is "taut".

That is all needed. Leave the bottles for several hours and use. The temperature under the clear plastic will be 10 C-40C higher depending on the intensity of the sun. In other words this becomes like a black car under hot sun (in the USA many children die from excessive heat inside these cars).

Let me know if you have any questions.


Posted on March 25, 2014, 12:33 am
by Thomas

is there any chance to see the scientific research/sources on this technique? this is something i would like to implement in a project i am working on but i need to be sure the science adds up before i do.


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