Drinking Sierra Water

No clear answer

Many threads about this including the recent http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=68224

and Rog's article from a few months ago

Two things to consider:

1. A healthy, non-immunocompromised adult can tolerate a certain degree contamination by the usual nasties (cryptosporidia, giardia, et alia). This is exactly why we evolved immune systems.

2. A bottle of water purification tablets weighs a fraction of nothing.

For my part, I've drank a lot of water directly from the source, and I've never had a problem. But I seem to have a pretty robust immune system, and for what it's worth, I only drink untreated water if it "seems clean" (which, I admit, is a terribly unscientific criterion for a scientist to use! heh). But I am also aware that each time I take a drink from a rushing mountain stream, I am playing a game of gastrointestinal Russian Roulette.

Last High Sierra trip I took:
5 days, 5 people, nobody treated a single liter of water that I am aware of.

Everybody was fine.

Skill?
Luck?
Divine intervention?
Science?
Stupidity?
Arrogance?

You decide.

To advocate for devil, Craig

If there is a small chance of getting sick from 1 day, say 1%

Then for one trip you'de have to be unlucky to get sick

But if you got sick 1 of every 20 trips you'de want to treat your water

To add to your list:

Statistics?

The higher up you are, the closer you are to the source and there is a less chance of having a dead animal upstream.

I just got over giardia that I'm pretty sure came from a recent sierra trip (SEKI). I usually don't filter and just try to get fast-moving, high-volume water up high. My luck ran out this time. The nausea and weakness I experienced were unpleasant enough that I am resolved to filter and treat my sierra water from now on. Not only is giardia unpleasant, but you don't want to have to put your body through a round of antibiotics if you can avoid it.