On my last group ride (40 miles) I drained four 24 oz bottles, I could have used at least one more. There's no refill point on the ride, so what you leave with is what you get. The first time I did the ride I had a bottle and a half, and was out less than halfway in. By the time I got home I thought I was going to pass out, since I'd stopped sweating long ago. It took me a few days to get completely hydrated again. Most of the other riders had two bottles and didn't run out of water, but I'll sweat sitting still on a cool day.