We have gone through a filter about every other 10-14 day trip. By the end of its second trip, or its only trip on our recent vacation, it was down to a trickle. The cost really adds up, but it seems many filters have the same issue. I will probably not use it at all in tannined water anymore. By about 12 liters, even after backflushing every 4, it was taking a really long time. Backflushing took quite a bit of effort, squeezing the clean water reservoir like a bagpipe until I got a little trickle instead of intermittent drips; never got a decent flow back. At about 20 liters, we were taking water back to camp in the reservoir bag and letting it hang in camp until it got 4+ liters done, about an hour or more. It works great at filtering, but you might need to factor in time and always carry a spare filter. Tannins seemed to be the big problem in clogging up the works. We have used it on 1-2 week kayak trips, filtering about 8 liters every other day or so. People in our group using other filters had some similar issues. Backflushed it again when we got home; did a 2 liter test with tap water, took 24 minutes , counting the few minutes it took to get the bubbles out and get it flowing.