Typical day today - 6 hours of pretty hard riding in the Peak, sweating a fair bit on the climbs. Had about 2l of Torq in the Camelbak, drank about 0.5l (plus a large coffee), Felt like I was drinking absolutely loads and was worried I was going to run out and really couldn't face taking on any more liquid as I felt awash with the stuff.
Funny old world, I'm feeling a little rough now, and was definitely fading towards the end of the ride (hence the large coffee to get me back up to Foxhouses!)
This is nothing new - back in my mid/late teens my dad and I would regularly do 12+hr walks up on Kinder or similar in the middle of a blazing hot summer day with no shade and less than a litre of water between us.
So how do I get my head round taking on more liquid? I hate drinking on the climbs, as it screws up my breathing. No way I'm going to try it on a descent, and the merest sip is usually all I actually "want" if I stop at the top or the bottom. I can generally force a mouthful down, but nothing more,(and I'm most likely to simply forget all together) and I'm still paranoid about running out.
I'm exactly the same on the road bike too - even when it's easy to see how much I have or haven't drunk. 40 or 50 miles, and I may have taken 2" out of the full bottle...