I'd carry just TWO items for water treatment. Neither is a filter.

1. SteriPen Adventurer UV light purifier> The SteriPen adventurer is light (it floats) and the Lithium batteries it uses are light and will last for at least 30 days of water treatment.

2. Katadyn Micropur chlorine dioxide tablets> Chlorine dioxide is used by your local water treatment plant. Properly used it has no taste. It is used as a backup for your SteriPen (one tiny tablet per liter). and to occassionaly sterilize your hydration bag.

A water filter is not what you want to be carrying as you struggle up thousands of feet of mountain, cursing every ounce you're carrying.

But, if you MUST carry a filter check out the new, small MSR filter coming out soon.

Eric