Corriamo saidMight want to read this article
At the other end of the spectrum, overhydrating can be even more dangerous than not drinking enough. Hyponatremia occurs when your fluid intake exceeds your rate of fluid loss from sweating, which results in low blood-sodium levels. Symptoms--nausea, disorientation, muscle weakness--can be similar to dehydration. Giving additional liquids to hyponatremic runners only exacerbates the problem by diluting their blood-salt levels even more, which can lead to coma and, in the worst cases, death.
From the article:""The new scientific evidence says that thirst will actually protect athletes from the hazards of both over- and underdrinking," says the IMMDA announcement."
At best, that is an oversimplification. The other day when I rode my bicycle 26 miles in 90F+ heat, mostly in the sun, I lost two pounds even though I drank a lot of water. At no time did I feel thirsty. The times when I have consumed insufficient water I experienced symptoms of dehydration without ever feeling thirsty. The symptoms were headache, fatigue, and dark urine.
In spite of what the article asserts, I fully believe that if one waits until one is thirsty before drinking water, one can become dehydrated. There is a limit to how fast the stomach can absorb water and if you wait until you are thirsty (and already dehydrated) before drinking water, your stomach may be unable to absorb water fast enough to recover from dehydration if you are sweating heavily. Drinking water faster than the stomach can absorb it causes other problems, i.e., difficulty breathing adequately and difficulty keeping the water down. It's hard to exercise vigorously while fighting regurgitation.
Also, it is a mistake to assume that everyone is the same. Some people may not experience thirst until they are significantly dehydrated whereas others may experience thirst much sooner.
Perhaps we all need to learn from experience how own bodies work and act accordingly.