30 - 40 miles and just two bottles? Yeah you might be getting a little dehydrated. Especially if the temps are up in the 90's. 30 - 33 miles is about as far as I can stretch 2 bottles in the heat. I usually take another bottle or stop and fill up if I'm going more than 25 miles on a hot day.
I know that there are some that think you get adapted to using just a little water, but the military finally figured out that you don't just before the 21'st century arrived. They found out that while one gets use to the bad feeling, their performance still stays bad.
And from my own experiences, anytime I don't drink enough to stay very well hydrated, I'm tired and fatigued for long after, sometimes days. If I stay very well hydrated I'm ready to go again after a short rest of 20 minutes. And I'm almost twice your age.
Weighing before and after a ride can tell you if you are hydrating well. Some say 2% less than what you started out is okay. But I find that too much for me. I'm usually less than a pound difference after any ride, 1½ lbs at the most.
You should consider consulting a medical professional though. If you aren't already, then you should be doing annual wellness checks with your doctor. Even when you don't have any issues.
Last edited by Iride01; 10-01-23 at 03:21 PM.