Eschewing fancy names, HydraPak adds their own filter to the small but growing choice of 42mm water filters that will connect to wide mouth bottles, bladders and flasks.
The Katadyn BeFree filter has been a favourite piece of gear for the past five years. Unsurprising as it is light, compact, easy to use and has been successful in preventing me from getting sick on trail
Three Points of the Compass 