I would not lug full water bottle(s) up a long steep climb if I could fill them not long after the climb
before we hit the base of long / steep climbs and knew there was a spot where we could fill water bottles - we often emptied our water bottles
Riding in the mountains on a hot day I sometimes start with around a gallon of water. A 70 oz Camelbak and 2 large bottles. When on the mtb I use a 100 oz Camelbak and I have paired that with one bottle.
I've drank over 220 ounces on a hot climbing ride. Hell, I used to drink 200 ounces at work when it was hot.