I have had some training in teaching Sodis to folks overseas and they are finding
it works even better than they expected, killing up to 100% of bacteria and viruses and that it also is working well at the high and cold elevations in Nepal.
At these higher elevations a clear 2 liter pop bottle disinfects clear water in
about 4 hours. This method is typically combined with sand filtering systems for
(long term home use) which themselves do an excellent job.
http://www.cawst.org/technology/watertreatment/filtration-biosand.php