Those must be thirsty folks! I should think two MSR filters would keep up with that. My advice: Fly in more beer. After all, hardly anyone drank water during the great age of seagoing exploration. It just didnt keep. So they drank beer. And thats what brought the Pilgrims ashore in a place where they didnt want to landthey were out of beer.
Anyway, what you clearly need is a Platypus CleanStream Gravity Filter System ($80). The name pretty much explains what it is: a water-filtering tool that uses gravity, not a pump action, to force water through a filter. The whole kit consists of two four-liter Platypus bags, some tubes, and a filter. You fill one bag with water from a lake or stream and hang it on a tree or something. Then, gravity forces the water through the filter and the other four-liter bag. It filters out dirt, protozoa, Giardia, and other stuff you dont want in the water.
The system is capable of filtering four liters of water in 2.5 minutes, and even though it probably slows down as the filter fills, that still should be plenty of output for your group.
Sawyer makes a similar system ($90) that also hits the four liters-in-three-minutes mark, and that actually has a slightly finer filter. You use your own bottles or bags for outflow.
Good fishing to you!
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