I just did a 15 miler in Idaho, at 85+ .. You need lots more than one bottle. I would start hydrating the night before, and not too much coffee ( diuretic) in the am. Then try and drink constantly the whole ride. I take lots of water ( 100oz ) in a camel bak and one bottle of Cytomax. I find the sport drink makes me nauseous and I drink constantly. Be sure you are peeing a lot, that will be the real indicator.
Irulan
2015 Liv Intrigue 2
Pro Mongoose Titanium Singlespeed
2012 Trek Madone 4.6 Compact SRAM