There rescuers said they were dehydrated so some part of their water purification system was not working. [/quote]

Somewhere it should be pointed out that when thirsty and dehydrated, it is important to drink water and stay hydrated, even if the water is polluted.

Two things: There is a good chance the water is fine to drink without treatment, especially in pristine or fairly pristine mountain environments when there are no obvious contaminating sources in the watershed (the higher you are the better).

Second - even if the water is polluted, it is far better to stave off the immediate effects of dehyrdation, which can all too soon render you DRT. If you incur a case of diabolical flunkabetis, you will at least be back in town where the situation can be treated.

Wandering around the mountains of Arizona in the 50s, I and my companions drank freely from untreated water sources on many occasions. Cases of water borne illness - exactly none. That was a time when very few were backpacking or climbing, so we may have been fortunate.

I would be more cautious today, but if there were no other way, I would drink up, stay hydrated, and deal with the consequences later.

Lastly, "dehydrated" is a very imprecise term, as has been pointed out. Most of us probably hike most of the time in what is actually a mildly dehydrated state.