Originally Posted by
DrIsotope
You should end every single one of these types of blanket statements with a hearty "YMMV." You live in Washington. It is currently 109º at my house right now, and today is one of the cooler days this week. I will sweat out up to 1 gallon per hour in high-temp, low-humidity conditions, without regard of effort or intensity. 30 mile ride? That might be four 25oz bottles. This morning I was out by 6am to stay ahead of some of the heat-- so I only drank 50oz (one bottle of water, one of 50/50 ice/Gatorade.) Only 91º arriving back at home. For me, in my current environment, not supplementing with something other than plain water is a recipe for disaster.
That said, I don't drink Gatorade October through May. Don't need it.
I'm very familiar with riding in heat. We have two states here, eastern and western. While I live in the western part, I frequently ride in the eastern part. Last week I rode 115 miles, 7000', over 2 mountain passes in temps up to 106°. I've climbed several mountain passes in 105° heat. The simple fact is that it's very difficult, even with training, to pass more than 1 liter an hour across the stomach lining. Which is a good thing:
https://www.medicalnewstoday.com/articles/318619.php
Your kidneys can eliminate about 5.3-7.4 gallons (20-28 liters) of water a day, but they can't get rid of more than 27-33 ounces (0.8-1.0 liters) per hour (14, 15). Therefore, in order to avoid hyponatremia symptoms, you should not drink more than 27-33 ounces (0.8-1.0 liters) of water per hour, on average (14).
This fact is pretty well-known by those who've ridden long distances in the heat. So what to do? If you get too dehydrated, you have to stop and rest in the shade while hydrating. Done it many times. That said, a little dehydration is not a bad thing. Performance actually increases up to about 1.5% dehydration.
As far as drinking plain water goes, of course as I've said above and many other times. I take Hammer Endurolytes as necessary. The important thing is neither to drink too much water (hyponatremia) or too much electrolyte (hypernatremia). Your body has very simple clues which tell you exactly how to respond.
Training in the heat is the best way to become heat tolerant. I make it a point to ride in the heat when I can.