So, what to do? Always filter water, of course. Beyond that, my policy is to consider its source. The closer I am to where the water got its starta glacier, a snowfield, a springthe less concerned I am about viruses. I don't think the Adirondacks area poses a particular risk, but its high usage by humans might warrant caution. If you are concerned, then it's prudent to treat the water with a virus-killing agent such as SweetWater Purifier ($9; www.msrcorp.com), a chlorine-based agent that kills just about anything that wiggles... in your water, that is.
Otherwise, you might want to consider one of Katadyn's filtration pumps, albeit a little more costly and bulky, but able to deliver quick, potable water on the go. The 11-ounce Katadyn Hiker ($60; www.katadyn.com) is a compact system that delivers about a liter a minute without too much effortgreat if you're in a group or don't fancy the aftertaste of some of the chemical treatments.
Get more water-filtration advice in Outside's 2004 Buyer's Guide.