I think it was an Army Captain a few years ago during Ranger training that died by drinking too much water.I have seen this a couple times while in the Army. The symptoms are very close to DE-hydration and very easy for medics to miss-diagnose. Of course the Armys answer for just about everything is "Drink water"
Dehydration occurs because one didn’t drink enough water the day before so the cells can absorb it from what I understand. Binge drinking water when feeling dehydrated does nothing but have bad results.
The old saying that you need a minimum of 8 glasses of water a day can be true for some but not others. Those with low activity levels and climate controlled work areas may require less while those working outside in the heat may need more. Electrolytes along with water is what’s important from what I’ve read.
Altitude also makes a difference in the amount of water a body needs.