I was listening to a BBC world report on 3rd world technologies, and heard about a simple method to" clean dirty water of bacteria, viruses and Micro organisms". Given the recent post on Puritabs, it seems like a good emergency alternative:

1/ Half fill a clean plastic bottle of the water you wish to drink.
2/Shake vigourouly for 20 seconds (with cap on <img src="/images/graemlins/smirk.gif" alt="" />) to oxygenate the water.
3/ Top up the bottle with more water.
4/ Leave in sunlight for 5-6 hours
5/ Drink

Ok, it might not be the long cool drink you were craving, nor be suitable for all conditions, but useful knowledge nevertheless.
Any comments?