I am surprised no body has mentioned a filtration system. If you NEED to purchase a filter and bladder I'd recommend the HydraPak. I have slowly transitioned over the past four years to this as I need to replace pieces. This
600ML fits in a hip pouch for easy access when crossing a creek so you can fill your water bottle with their
water filter. If you backwash and take care of the filter it will last you a long time. I have two just encase one fails, but I have used one extensively and its flow rate hasn't slowed at all. They also make a
3L storage that also fits the water filter. While getting links I noticed this new item -
Seeker+3L I'm not sure what could make it UL, but it appears you get the filter and reservoir for $60 which saves you some cash