He should have ridden an ST!
Besides, he's too old to be riding!!
But, yeah! Keep the fluids up. Both articles cover the essentials (excepts you don't need electrolytes all the time, not even most of the time).
My first symptoms of being behind the hydration curve is a headache. Once it moves in, it can take a day to shake off completely.
The comment about very cold water is true, but body temperature water isn't at all refreshing. Like everything, moderation is best, and
cool water will lower the core temperature without causing cramps.