The hydration thing came up just a few days ago with a friend of mine who was drinking tons of water, peeing clear, and still feeling off, slightly light-headed, and thirsty.
When I pressed further, I learned that she'd been avoiding salt for health reasons and eating a very alkaline diet (salads, few carbs and no salt). She said she also preferred not to cook with salt.
The irony, is that this kind of diet is optimal (but complicated) for static apnea, when you are basically at 1 atm and don't have to swim through a rapid decrease in pressure (or stand up quickly).
It sucks for staying conscious.
I had been in a similar situation many years ago without knowing it. Plain and simple, you can't absorb enough water without proper electrolytes.
Sodium
Potassium
Chloride
Bicarbonate
Bicarbonate plays a big role in maintaining normal levels of pH in the body. :martial
Peeing clear pee, for lack of a better term, is only a rough indication of hydration assuming you've got good electrolyte balance. It means squat it you are nutritionally and otherwise deprived. If you are still thirsty, that's a bad sign.
Eric reminded me that the general public often hears of reducing salt intake to combat high blood pressure. As he put it, roughly paraphrased, In order to combat hypertension, we're going to give you drugs and put you on a diet that makes you dehydrated, thereby relieving blood pressure. Never mind the effects of chronic dehydration!
We've often joked that we should be sponsored by Kettle Chips. Several years ago we started eating them between dive sessions and found ourselves rejuvenated. Hmmm. Salt and potatoes.
Per 28g serving (we'd eat half a bag or more each!)
Sodium 190mg
Potassium 400mg
Chloride content (not listed)
Still swear by them.
Anyway, bring chips next time! (and oral rehydration salts)
Pete