if you're with your family get something that will easily filter 5+ liters. the gravity bags are pretty good, i've used a katadyn one before but i'm sure there are other brands. the sawyer filter is one of the best for backpacking, very compact, but is not the right filter if you only buy the squeeze bag with the filter, it will take so long to filter enough water for your whole family. i think there are setups for the sawyer that you can do a gravity system though and that fixes the issue. i wouldn't get a UV purifier or a hand-pump filter. not because they are not effective and safe, but because they work better as individual filters and might be a pain in the ass for a full family.