[pct-l] How much water????

[Ellen Shopes]

I've been out hiking a section of the Arizona Trail this weekend, or I would 
have responded sooner.

First, I have to echo the sage advice of some of the responders.  It's too 
soon to know what the daily heat load will be or how much water will be 
available.
Now, for a little 'primer' on humans and how they adapt to hot environments. 
This will seem to contradict what some others have said, so here is a bit of 
my background.  In my time at Grand Canyon, I organized/implemented a study 
of heat illnesses that occurred each summer.  Many of the public education 
programs and SAR practices at the canyon stem from these years.

1.  Heat illnesses (heat exhaustion, heat stroke, exercise-induced 
hyponatremia, heat cramps) start to appear when daily high temperatures 
reach 85 degrees.

2.  Heat adaptation.  Humans thermoregulate (maintain their body 
temperature) in a hot environment by sweating.  Over the course of a week or 
two, one does adapt to the heat, but does so by SWEATING MORE, not less.  As 
part of the acclimitization process, the sweat will contain less sodium 
(salt).  Since overall sweat production is more, total sodium losses are 
probably about the same in heat-adapted and non-heat-adapted individuals.

3.  In a hot environment, average losses are about 1 liter per hour (of 
exercise).  Obviously, losses are much less sitting in the shade.  This 
explains how valuable it can be to sit out the hot parts of the day.  For 
the record keepers in this group, the greatest sweat loss per hour (in a guy 
on a treadmill working at maximum intensity in a heat/humidity controlled 
room; he was wearing a specially designed suit that collected his sweat) was 
2 liters.  It was felt by the researchers at the time that the runner would 
not have been able to continue to work at that intensity for much longer.

4.  Dehydration affects performance.  Studies that have looked at 
performance show that losses as small as 2% effect performance.  The sense 
of thirst does not kick in until losses of 3-5%, so is not a reliable 
indicator of when to drink.  I might also mention that a small but 
appreciable number of hikers have been having problems with kidney stones 
on-trail.  I suspect that the stones are forming in concentrated urine 
during the hot sections of trail, then not becoming apparent until the 
stones start their transit down the ureters to the bladder days and weeks 
later.

5.  As others have mentioned, in the dry heat of the desert, one often feels 
fairly comfortable--sweat doesn't soak the clothes (as much) as it does in 
more humid environments, or drip off the head as much.  But the losses are 
still accrued and need to be replaced.  Although it's not full-proof, one of 
the best ways to know if you are drinking enough is to monitor your urine. 
If it is yellow-tinged (not deep yellow, tea-colored, nor orange) you are 
probably drinking enough.  You can test this by trying some hikes when the 
temps are over 85, or on a treadmill somewhere where you can set the 
thermostat at that level.  Although humidity will make the work less 
comfortable, it will not have a significant impact on your losses.

A final word: when hiking in the heat of the desert, the heaviest thing in 
your pack should be water!  Look for other ways to save weight.  Don't short 
yourself on water; it could cost you your life!
Elderly Ellen
(OK I'll get off my soapbox now!)
(See you on the trail in 2010 with my ton of water!)

----- Original Message ----- 
From: "CRYSTAL NEZGODA" <littlevixsin at gmail.com>
To: "pct-l" <pct-l at backcountry.net>
Sent: Friday, September 11, 2009 11:44 AM
Subject: [pct-l] How much water????


>I am planning a section A and B hike for next season, the green pct book
> says to bring atleast 8 liters of water per day... so I was wondering if 
> you
> guys could tell me about your experience with the desert section and water
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