MSR Sweetwater Purifer system, about $75.00 from REI. Easy to pump and clean. Filters to .2 microns, then use included chlorine drops to purify. Micro-pur tabs as a back up. System is efficient and cost effective. I've used the Sweetwater since the early 90's for week long, fly-in fishing trips in Northern Ontario. Early spring, water temps from 40-mid 50's F, groups of up to 12. No beaver fever, no drama. Only additional item I bring is an extra filter.