Bob Rockwell always dipped and drank everywhere in the Sierra. He wrote this: 60,000 Liters of Water Consumed -- Untreated, and a more scientific study:


Giardia lamblia and Giardiasis With Particular Attention to the Sierra Nevada By Robert L. Rockwell

I don't think you could find any contaminated water on the HST. I've hiked most of it, and never treated any water.