There's no one size fits all for this. I'm an overweight senior. I went out last night (mid 90's and high humidity) with two 1 liter water bottles filled with water+electrolytes. Half way through my ride I refilled them. Drank that up. Then I stopped at a coffee shop, drank an ice water plus a 20 ounce Sprite. I finished a 19 mile ride. Yet I still had a wicked head ache when I got home. I think I'll wait till Sunday when the heat is supposed to break before I venture out again.