Okay, so over a course of 45 years I have done it all when it comes to treating water - boil, chlorine, iodine, pumps, steri-pens, and now the gravity feed. They all have their problems, even this, but of all of them I find GravityWorks the easiest. No pumping, no long waits, no foul taste, and no batteries to remember (packing extras in cold weather).The down side to this is also the plus side - you fill up a "dirty water" reservoir with untreated water, put the outflow tube into either a bottle or another reservoir, and raise the "dirty" water higher than the clean container, then wait for it to drain. This means two things:Carrying a reservoir for the dirty water, and keep it away from anything you don't want contaminated. I carry a 1-gal ziplok bag and stash the dirty container into it between uses. MARK THE DIRTY CONTAINER SO YOU DON'T CONFUSE THEM!Depending on what you use for the clean water, it may not be easy to do. A bottle stands on its own, but a reservoir doesn't.
from Somewhere in the Laurel Highlands...when they can find me,
We(3 buddies and myself) took this filter into the Enchantments, in Washington state. It easily kept clean water coming all weekend long. The flow rate is respectable, and no sore arm from pumping or falling into a lake while crouched over trying to find a good silt free spot to filter from, just scoop up the water bring it back to camp and voila.