I agree with what Izzy had said about carrying a 32 oz bottle, this is why I harp on the Guyot Designs stainless steel backpacker model bottle, it's 32 oz which is 1 dose with a steripen or 1 tablet with a Katadyne micropur tablet (backup for the steripen). It makes it easy for treating and in a pinch you can boil water in it as well plus no plastic taste or leaching. Best thing since fried chicken for me.

http://www.guyotdesigns.com/Product-Bottles