This is the 50+ board ,right? The discussion on hydration here makes about as much sense as trusting the stop light enough to blindly cross the street.
Not paying attention to appropriate hydration especially in this age group with its morbidities conditions and medications is disturbing.
People have GPS, speedometers, power meters, and cadence meters and don't bother to look at the scale.
After your second quart you need to start using your brain.
Sadly one of the signs of disorders of hydration and thermoregulation is impaired thinking.
If you're thinking is impaired before you start, this is not considered a good thing.
Trusting your thirst is better than being entirely stupid, that still does not hit the threshold of actually being halfway intelligent
And the only doctor you're going to need , was the one on the HMS Beagle.
Heatstroke is real and the risk gets worse with age and other impairments.
Ill considered hydration strategies that lack balance are a big risk.
If you were pushing hard enough it's hot enough or it's far enough that you're going beyond 2 quarts and/or a quart an hour, you need a well thought out plan and some real science.
it's rough enough trying to avoid brain injuries from the outside. your kidneys are only so smart.