I do this 50 mile run frequently in 3 hours on (3-4) .75 liter water bottles. I am 185# and 6 ft, no fat. This is at temperatures up to F95 and humidity above 50%.
My wife and I did this same run today. Temperature was F95, humidity 50%. BTW, she is 140# and 5'3".
I made a mistake of not watching my wife. She does this same run often without a problem. I failed to observe that she drank over one gallon of water. She got very bloated after 35 miles and felt very ill. I mean very ill!
We had to stop at a gas station to cool her off and feed her Gatorade. We managed to complete the ride slowly. She was OK one hour later and we had a nice dinner with wine.
The lesson to be remembered is: Do not drink one gallon of water without adding electrolytes. Your system may rebel and it is serious.