Wife and I went climbing in the High Atlas this year and did a load of research on this…..
There are several levels (and accompanying levels of cost):
1. Basic ones that just filter out particulates
2. Filters that have specified pore sizes down to 0.1micron will also filter out Bacteria, protozoa etc. (BUT not viruses)
3. To kill viruses some filters have an activated ion part to the filter – BUT it’s not 100% and they are very expensive.
We (and everyone else on the trip) went for option 2 and then used either purification tablets or drops – the drops are better as it’s a two part system and the activator only works for a while then breaks down to be almost tasteless. The ones we used were called “Biox Aqua” and you can get them online from several outdoors shops
We have the Platypus inline filter system – comes with two large platypus reservoirs (marked “clean” and “dirty” just to be on the safe side) and it worked great – the reservoirs have press lock tops so you can get them fully open to clean or to scoop up water in a river or stream and you hang the dirty one up and let gravity pull it through the inline filter to the clean reservoir.
The biox drops were good although a bit fiddly – you have to count out a set number of drops from each of the two parts then let them mix for 10min before chucking them in the clean filtered water (I did wonder if a v. small syringe would be a better adaption but didn’t get chance to try it). The purification tablets were faster and easier but tasted much much worse – and over two weeks hard walking and climbing in high temps the chlorine would do your stomach in I think.
We survived two weeks using this system purifying at least 5+ liters a day (its damn hot in Aug/Sept in Morocco) and we were fine.
Badger