Although there have been reports in the Journal of the Wilderness Medical Society on sampling of several areas (mostly in the Sierra's) a map is my primary tool. I use the protocol described in the Field Guide to Wilderness Medicine by Auerbach, Donner and Weiss. The key is what is upstream of you. If there is agricultural land, built up areas (human habitation) or heavy use recreation areas - suspect contamination. The CDC reports about 300,000 cases of cryptosporides each year in the US. Most of them are associated with direct transfer but that tells me that if man is present crypto probably is too.

In high alpine areas I sometimes use water without treatment. If I do use treatment it is usually filtering. If there is some human presence (a common campsite in the wilderness) above me I use one of the above methods. If there is a very heavy use area (campsites on the AT, cattle or sheep grazing areas, a small town) I always use a technique (whatever one I might be carrying). More than that (Florida, 3rd world countries, etc.) I use a 2 step process (usually filtering followed by chlorine or UV).

Although treatment is, I think, a good idea, most wilderness infections come from poor sanitation - not properly washing hands, latrines too close to campsites (not necessarily your latrine), etc., not from contaminated water.

Respectfully,

Jerry