Hey, Xelif, good research, I've copied your info to my Water Purification folder. Thanks for sharing it here, and please keep us updated on what you come up with regarding proper or improper containers for UV treatment. I will pass your info on to the staff at Living Waters International. Peoples health and even their lives are at stake in the third world countries where every purification process must be made available to them asap.

Ya see that's why I like this group of people, nobody gets upset when you share, discuss, (or even disagree over) knowledge.

I'm glad you're bringing it up with people who are in a position to use the information. (Slow-sand biofilters originally got me interested in water purification!)

I'm afraid all I did was muddy the waters, so to speak. I read the SODIS site itself, which has a wealth of referenced pdf files I'm just sinking my teeth into. First off, don't doubt the in-the-field SODIS tests that prove the method works. It's pretty convincing.

UV wavelengths extend from 400nm to, well, 1nm. UV-C is the shortest wavelength under discussion, and it's the best at disrupting DNA, etc. It's also, interestingly, blocked by ozone such that we don't see much at the surface. That's why the ozone layer is useful, and holes in it less useful. The ozone is at least partly generated via the energy released by UV interactions in the upper atmosphere.

The SteriPen supposedly pumps out primarily UV-C. Sunlight that reaches us is 98.7% UV-A, from 320nm to 400nm. (http://en.wikipedia.org/wiki/Ultraviolet)

To answer the question I originally brought up: None of our facts are wrong!


Page 2 has a depiction of UV absorption. The relevant information is that PET bottles absorb everything BELOW UV-A light. That means they absorb all the UV wavelengths that get soaked up by the ozone layer <img src="/forums/images/graemlins/grin.gif" alt="" /> In fact, almost all plastics do absorb UV-C light, just like the SteriPen states, and transmit UV-A light, like the SODIS site states.

SODIS states all plastics have, to some degree, UV absorbers such as plasticizers and dyes in them. PET bottles are best as you already know - and they've looked at the UV absorbance issue to some extent. For example, they warn that the older and more damaged the bottles are, the less UV gets through. That is, perhaps, the real issue with UV light and containers. I know that UV is the primary degrader of plastic and will eventually trash almost anything plastic left out in the sun, once it overwhelms any built-in dyes or absorbers.

Again, I'm really, really glad you brought all this up. I learned quite a bit - I just hope I'm managing to convey this in a halfway coherent form. This too is why I like this site, we pleasantly discuss things without rancor!

I'm going to have to think about how wonderful this method of disinfection is <img src="/forums/images/graemlins/laugh.gif" alt="" /> perhaps even lighter than the lightest ultralighter's dream <img src="/forums/images/graemlins/grin.gif" alt="" /> (don't tell them over on BPL)
- John