I posted this in another thread so i copied it. I just bought a sawyer 4 liter filter system which is a two bag gravity fed system. You have a dirty water bag which runs through an inline filter to the clean water bag. So you can filter 4 liters into the clean bag and then fill the dirty bag with another 4 so you have 8 liters total which is great if you are not camping close to a water source. The clean bag has a drinking tube so it also serves as a water bladder. so now I have a 4 liter bladder which is more than enough for all day hunts as well as long hot hikes with my dog. They have a million gallon guarantee and there is rarely a need to backwash these filters.
Two years ago I started with a Katadyn filter bottle. it was totally worthless and ended up using the Iodine tablets I brought as a backup.
This time I just used the 2-part Iodine treatment.
I have heard a lot of good reports on the sawyer system.