Steve has asked me to post on my experience with drinking water on my recent JMT hike, especially the Whitney section, and I am happy to do so.
Especially now that the usual incubation period for giardiasis has passed.
Long and short of it is, I used no water treatment of any kind, except filtering through my teeth, for over 99 percent of the trip. The less than one percent was for stagnant pools in low or no-flow situations, which happened exactly twice: on Sunrise Creek and around Long Meadow, both between Yos valley and Cathedral pass, an otherwise extremely dry stretch. Also, to paraphrase W.C. Fields, fish were dying in it.
Much of the time, when I had a pretty good idea of where water was, I didn't carry any either, but just stopped at available opportunities - crossings, springs, seeps, lakes - dipped my cup and sipped. For one stretch early on, when for other reasons I knew my electrolytes were out of balance and I had trouble hydrating, I carried ERG or water with electrolyte tabs added, but this was for the convenience of not having to add powder or tabs to each cup. After the halfway point at MTR, I carried very little.
I learned that my Sierra cup is now reverently considered Old School, having passed in my lifetime through stages of Conventional, Traditional, Cliche, Outdated and Unheard-of. As a matter of fact, I don't recall seeing another one on my trip.
Oh, sure, there have been cases of giardiasis contracted in the mountains. In exactly none that I have ever heard of has poor camp hygiene been eliminated as the likely cause.
In a normally wet year, I would have carried even less, but there were stretches this year, notably in the northern half of the trail, of up to five waterless miles.
In the Whitney zone I D&S with confidence, and especially looked forward to doing so at SB 23, everywhere there was access to Lone Pine Creek and most of all at the Bighorn Park spring.
At some locations, my water consumption got me some looks, and even comments. At Duck Creek, south of Red's, a group from Santa Barbara watched and just smiled as I dipped from the creek they were busy bagging and squeezing and pumping and steripenning, as if they expected me to keel over, clawing at m throat and screaming to be put out of my misery any second. Later, at a lakeside outlet stream, they asked me how my untreated water was sitting.
Too bad. The mythology of giardia has made Katydyn, PUR, MSR and others a ton of money, and I am sure all that tech is necessary in some of the country, but experience proves it completely unnecessary where I have gone in the Sierra, and it has ruined for thousands the simple joy of sipping from a mountain stream.
So I wash my hands. Dip my cup. In that order.
As always, your mileage may vary.
But in this case, I doubt it.