"I think you'll find that almost all plastic blocks UV quite well - the SteriPen in fact depends on this in order to prevent burning you with UV light. So, the plastic bag in sunlight doesn't do anything other than warm the water and degrade the plastic a little bit faster."
Sorry, plastic does not block UV rays. However, plastic coated with Nanoscale titanium dioxide particles will block UV. My plastic drink bottles that I use on the trail to UV treat my water with are not coated with Nanoscale titanium dioxide particles. The SteraPen's plastic design is for strength and weight savings, not to block the UV rays. Unless, of course, the SteraPen's plastic handle area is coated with (everybody say it out loud) Nanoscale titanium dioxide particles.
I learned about the UV treatment while studying under Harry Lee Westmoreland Jr.s Living Water International. I have certification in water well drilling and multiple purification techniques of raw and contaminated water for third world country inhabitants. All part of my volunteer missionary field training that I took upon myself so I could be of use to people where ever I go. I'm a Christian, but not a flat liner, as some would mistakenly think.
Living Water International web site: http://www.water.cc
Here ya go, Xelif , here's one of many articles regarding UV treatment of water in simple plastic jugs. This particular article is taken from: http://www.who.int/water_sanitation_health/dwq/wsh0207/en/index4.html
"Solar treatment by combined UV and thermal effects
Treatment to control waterborne microbial contaminants by exposure to sunlight in clear vessels that allows the combined germicidal effects of both UV radiation and heat also has been developed, evaluated and put into field practice (Acra et al., 1984; Conroy et al., 1996; 1996; 1999; Joyce et al., 1996; McGuigugan et al., 1998; 1999; Sommer et al., 1997; Wegelin and Sommer, 1998; Wegelin et al., 1994). A number of different solar treatment systems have been described, but one of the technically simplest and most practical and economical is the SODIS system developed by scientists at the Swiss Federal Agency for Environmental Science and Technology (EAWAG) and its many collaborators and partners.
The SODIS system consists of three basic steps: (1) removing solids from highly turbid (>30 NTU) water by settling or filtration, if necessary, (2) placing low turbidity (<30 NTU) water in clear plastic bottles of 1-2 liter volume (usually discarded beverage bottles and preferably painted black on one side), and (3) aerating (oxygenating) the water by vigorous shaking in contact with air, and (4) exposing the filled, aerated bottles to full sunlight for about 5 hours (or longer if only part sunlight). The water is exposed to UV radiation in sunlight, primarily UV-A and it becomes heated; both effects contribute to the inactivation of waterborne microbes. The system is suitable for treating small volumes of water (<10L), especially if the water has relatively low turbidity (<30 NTU).
Clear plastic bottles are considered preferable by some workers over glass because they are lighter, less likely to break, and less costly. Bottles made of polyethylene terephthlate (PET) are preferred to those made of polyvinylchloride (PVC), other plastics and most types of glass because they are less likely to leach harmful constituents into the water. In addition, they are lightweight, relatively unbreakable, chemically stable and not likely to impart tastes and odors to the water." (end article)
Also from: http://www.ciwem.org/policy/policies/chlorine_disinfection_of_water_supplies.asp
6. Generally, viruses are more resistant to chlorine than bacteria.
7. Harmful organisms can be shielded by particulates, therefore chlorination should be linked to a low water turbidity standard. This may require pre-treatment (filtration) processes if source waters are turbid.
Xelif wrote: "Finally, the dead bacteria isn't going to hurt you. Viruses with disrupted genomes won't do much either. It is a bit creepy though. Just a bit of extra protein and carbohydrates though ;-)
Brumfield wrote: I prefer good Tequila with a dead Mescal worm over dead bacteria, but... each to his own favorite drink. <img src="/forums/images/graemlins/grin.gif" alt="" />
Xelif wrote: Bacteria that produces persistent toxins (such as botulism) aren't likely to be in our wild drinking sources."
Brumfield wrote: Unless you live where there are zero birds... ya better look here: http://www.google.com/search?q=botulism+in+water&btnG=Search&hl=en
And from wild life: http://www.google.com/search?hl=en&a...G=Google+Search
Xelif wrote: I like my SteriPen and I use chlorine tablets as an alternative, just thought I might comment on this.
I use the BIG free SteraPen in the sky, (no batteries required) and I use chlorine dioxide too, but I can't help but wonder why quality water filter companies always mention that one of their filter's main purpose is to REMOVE chlorine? <img src="/forums/images/graemlins/confused.gif" alt="" /> So I chlorinate before filtering now. Brum <img src="/forums/images/graemlins/smile.gif" alt="" />