I have one that is a filter. But it is exactly that: A FILTER. It will remove Gardia and Cryptosporidium with it's 0.2 micro filter. It will not remove virus's. Fortunatly most viruses are easy to kill with chemical purification. It is intended for use in situations where I cannot (for whatever reason) treat the water with MP-1 tablets or I am limited to whatever puri-tabs I can obtain locally. That would probably mean Iodine or Chlorine tablets. Possibly using a Vitamin C tablet from the local chemists as a neutralising tablet in order to make it drinkable afterwards.

So the plan is: Fill the bottle. Tab it. Neutralise it before drinking and than suck the water up through the straw from the bottle.