The Katadyn Hiker or Hiker pro are light and very effective. You may want to also consider a Steripen. It is also very effective, compact and light. The Steripen uses ultraviolet light to kill all of the bugs, so all you do is turn it on and stir the water with it until the light goes out. I don't recommend the tablets because they make the water taste so bad. Many hikers on Whitney don't treat their water, since water quality on the mountain is generally very good. Personally, I always treat water taken from surface water before I drink it. Better safe than sorry!
