Reliability / Effectiveness
Based on the manufacturers' specifications, we evaluated which filters were effective against certain contaminants. The main difference is whether they treat for Cryptosporidium and if they can purify out viruses. We did rigorous field testing and put each product to the test for durability with regular backcountry use to see where these products fail with use. We also researched online by reading the product reviews to see if there were trends in products based on other users.
Ease of Use
We used the products — a lot and in side by side comparisons, in the front and backcountry. We determined how easy there were to use and in what ways.
We evaluated each filter on the quantity of water each cartridge or purification method could treat before it ran out or needed replacement based on the manufacturer's specifications. We also evaluated how much each water each product could hold at a time which significantly affects its treatment capacity. If it can only hold 20 ounces at a time its capacity is reduced.
We time-tested each product by filling a liter bottle. The pump filters were a bit more subjective in this department, as our tester's time was based on how quickly they could pump and we averaged the time of 3 fills versus just doing it once.
We did not take the manufacturer's word for it in this department, instead of testing these products on our scale with all the components we would want or need to bring with us in the backcountry.