There are two types of water-based concerns while doing strenuous activity in the desert: dehydration and hyponatremia.
Dehydration occurs when your body is not getting enough water, and is the most common. Symptoms include irritability, headache, lack of energy, bright yellow/orange and infrequent urine. You lose water while you sweat, but in hot climates you don't necessarily notice since it evaporates so readily. Along with that water, you also lose electrolytes (salts and minerals) that your body needs. Lose too much of those, and drink too much water without replacing them, and you tip the balance in the direction of hyponatremia.
Hyponatremia (which the questions linked allude to) is a very serious condition on the other end of the scale that occurs when one drinks too much water without replacing the salts sweated out. It is affecting more and more people exerting themselves in hot climates due to our increasingly "sodium free!" diets.
Your body needs salt to function, and as you sweat, you lose that salt (and other nutrients) which water alone will not replace. Usually this isn't a big issue, and the salts get replaced with meals etc. But if you are sweating a lot and drinking anything (water or sports beverages) to excess, hyponatremia can set in.
Symptoms of hyponatremia include headache, nausia, irritibility, disorientation, dizzyness, vomiting, seaizures, coma and death. It is not to be taken lightly. Interestingly, some of these symptoms are the same as dehydration... but if you are experiencing the above while your urine is still clear and copious (likely because you have dutifully been pounding drinks down) it is probably hyponatremia.
- Regulate Water Intake : if your urine is clear and copious, chances are you are sufficiently hydrated. Ease back, even if you are thirsty.
- Eat Food. Salty food. Pretzels, nuts, trail mix, granola bars... anything you can find. The general advice among Grand Canyon guides is eat regularly throughout the day. If you do that, drinking plain, clear delicious water is fine. However, drinking only sports beverages and not eating is setting you up for trouble**
**Sidebar: Several sources suggest that sports beverages can actually increase risk of hyponatremia since their deliciously tasty tangy sweetness can cause one to drink more fluid than they would otherwise.
Advice from the doctor at the Grand Canyon clinic as reported in the Wilderness Medicine Institute regarding the issue:
Prevention is a matter of being sensible, which is so often
the case. Drink lots, yes, but eat salty foods regularly while
exercising in heat. "Relying on electrolyte replacement drinks alone,"
writes Dr. Myers, "is absolutely ill advised."
If a patient is approaching a hyponatremic state:
Dr. Myers warns, that giving oral electrolyte replacement drinks, such
as Gatorade, alone might damage the patient. These drinks are so low
in sodium and so high in water the dilutional imbalance may be
As a final note, this is not to advocate NOT drinking water while hiking, since Dehydration is just as bad and far more common. Be smart. Drink what you need, but not more. Be aware of what you body is doing.
Additional sources, all of which authoritatively conclude the sports beverages do not prevent the onset of hyponatremia. If you are drinking to much, it is too much, regardless of what you are drinking.
Consensus Statement of the 1st International Exercise-Associated Hyponatremia Consensus Development Conference, Cape Town, South Africa 2005:
Ingestion of electrolyte-containing sports drinks does not prevent the
development of EAH in athletes who drink to excess.
Clinical Journal of Sports Medicine:
The total cups of water (p=.004), electrolyte/carbohydrate solution
(p=.005) and total amount of fluid ingested (p<.001) were
significantly higher in [Hyponatremic] compared to [Non Hyponatremic]
runners and the degree of hyponatremia was related in a dose dependant
[Bob Murray, PhD and the longtime director of the Gatorade Sports Science
Institute] acknowledges that neither Gatorade's new Endurance Formula
nor the traditional Thirst Quencher will prevent hyponatremia if a
runner consumes too much sports drink during a marathon.
"We can't add more sodium because the research clearly shows that too
much sodium actually impedes hydration," he says.
Rock and Roll Marathon page:
Even Gatorade, Poweraide and all Sports Drinks or IV NS will therefore
increase free water and lower serum sodium
Tangentially related study in Schizophrenic Patients:
Conclusion: Substitution of electrolyte-containing beverages is not
likely to prevent water intoxication.