I can vouch for the MSR filters. I have a handheld one that screws onto a nalgene bottle. takes only a few seconds and we always have a few liters spare. I also believe MSR makes a gravity filtration system that works for larger groups.
Clean safe water is a necessity -- I never go on any trip without my filter.
Cheese cloth and boiling works but, it's work.
Another option that's gaining a lot of traction is UV light filtering. I believe CamelBak has a UV water bottle. That may be up-scalable for the amounts you are talking about, and is very quick provided you have a pre-filter for particulates.
How I Get Around:
2012 Jeep Wrangler Rubicon Unlimited, Gobi Stealth roof rack, Tepui Kukenam tent, German Shepherd "LOOK ITS A PERSON" system.
2011 Triumph Tiger 800 XC, Givi cargo rack, home-made Pelican panniers.
Clark's Desert Boots Heel-toe express