im off traveling for 18 months rtw trekking and backing, india,nepak tibet s america, blar blar blar.
im looking for a water filter and not sure which one to go for?

im looking at geting either Katadyn Pocket Filter or a MSR water works.

which is best for traveling. do i still need to use chemicals with the filters or can i get away with out them?

Don't get the small Katadyn one with a plastic plunger thing - I used to have one, and it snapped under pressure.

For filtering water in the jungle, I used an army PWP kit (personal water purifier - little thing that you set up to screw onto a 58 pattern water bottle, then it acts as a filtering funnel) - very efficient, and best of all, no physical effort required to filter water - you just pour it into the top, no pumping required.

Whether or not you need chemicals as well depends on your filter. You'll need one that filters viruses as well as other contamination, otherwise iodine is recommended.

If your constantly filtering for 18 months, remember that filters get clogged, need cleaning, you may need replacement bits for them etc as well - check availability before you go, or carry spares if you're not going to be passing through anywhere likely to sell such things. If you're just taking the filter as back up, and are going to drink bottled water when available, this isn't really a problem.

HTH
C

If you need a back up have a look at Aquamira.Kills all the nasties and no aftertaste.Two small bottles weight about 3oz treats 120 litres worth having with you if you have a problem getting spares for your filter.

The APT(i) is a British water purifier/filter that's been around for a few years. It's a personal-use rather than a group use model. Costs £40 for a 750ml bottle with a screw cap which houses a 2 micron carbon activated filter (for keeping out all water borne bacteria)around which is an iodine shroud that kills off water borne viruses. It is soooo easy to use: simply fill the bottle (even dirty pond water if that's all there is), screw the top back on, wait 15 minutes if you're in a viral risk area, open the sports cap type nozzle and you're away. The flow rate is really good, like drinking out of a sports bottle really. It's been approved by the London School of Tropical Hygiene (or is it the other one, I always get confused). The filter lasts for about 350lt worth but you can get spare filters anyway.

I use a Pre Mac MWP purifier that has been with me all over the place. It filters with charcoal etc and is then filtered through iodine crystals to leave a residual amount in the water. It does leave a faint smell but no taste. Each set of cartridges will treat 250 litres of water before needing replacing.
the pump is about £65
the refills are about £25
Its really small and light, bombproof contruction (the M in MWP stands for military!) is is really simple to use and clean, with a reasonable flow rate. I can fill my standard british army water bottles in about 2 minutes. Leave the water for 5-7 minutes to let the iodine do its job and away you go!
Have a great time and remember....DON'T DRINK THE WATER :o)