Again, this is not purification, this is an attempt at disinfection. This is ridiculously far below the standards used for public drinking water, and we don't call our water "purified".
It sounds like you have a bunch of practical experience in municipal water treatment. Lots of great info in this thread. :thumbup:
The purification/disinfection terminology is a huge source of confusion, imo, and that article above doesn't help the matter any. As I understand it, "purifying" is removing everything (or as much as technologically possible), and "disinfection" is inactivation of harmful or potentially harmful microorganisms in the water.
I agree that truly "purified" water (say milli-q or more pure) requires much, much higher levels of treatment than anything we would do for drinking water. There's just no point in removing everything unless you're doing some sort of ion sensitive research.
As far as SODIS disinfection, there was a paper in the journal Microbiology (link at
http://www.sodis.ch/index_EN) that showed the SODIS method can get between 3 and 6 log reduction in bacteria with 2500 kJ/m2 of natural uv exposure. For those not water treatment inclined, that means 1,000x to 1,000,000x fewer bacteria after 8hrs of good sun. The range has to do with sun intensity on a given day. I think municipal water in the US requires 6 log or better.
They also showed that it is actually better to store the treated water overnight before drinking, b/c many cells partially damaged by UV will continue to die overnight. The cells do seem to die (rather than just inactivation), essentially from starvation after uv damage to the way they get their energy.
A different paper has shown that UV does not work as well against oocysts like Giarida or Cryptosporidium. They found only about 50% to 90% reduction in these, depending on cloudiness of the water.
As others have said, it's much, much better than doing nothing. And given the right conditions, it's a great way to go for bacterial disinfection.
