I stumbled across this article on pasteurizing water and found some interesting info that I haven't seen in any of the survival literature I've read in the past.

Key points:

1. water only needs to be heated to 150 degF to kill biological pathogens. Boiling is not necessary, only enough temperature for pasteurization.

2. water can be subjected to intense sunlight via a clear container and achieve pasteurization in less than 1 day if the weather is warm & sunny.

I haven't cross-checked the info yet but the article has some pretty good cites with it.

I think this is good stuff to know for the survivor. Perhaps the addition of a simple non-glass thermometer to the survival kit would be reasonable. Point #1 would save time & fire fuel, and point #2 would give confidence to the survivor who has no other purification methods available.