I just finished a day hike. I started out with what I thought was 3 liters, but actually 2.5. I drank about 2 before pumping water at trail camp. I headed up to the summit from there with 2.5 liters. I drank less than 2 liters the rest of the total hike (back to portal). Of course, it started pouring and hailing, so I was a little distracted from drinking.
That said, I don't drink a lot of water normally. I really tried to drink a lot on this hike to reduce signs of AMS. But I'm a cactus, apparently. If you tend to drink a lot, then I think I'd be prepared to carry a lot. If you don't, you'll probably be fine heading from trail camp to the summit with 3 liters. There was what seemed like a million places to pump water between the portal and trail camp, so toting a lot of water isn't too necessary through there.
