I'm a big drinker. If I do an hour bike ride I'll go through most of a 2 liter Camelbak. On any run over 30 minutes, I'll carry water. You may not be getting as much as it seems if you just have one water bottle.
Along with some of you, I lose a lot of salt in my sweat. I now order a custom blend from Infinit Nutrition to get the extra salt I need in my drinks without the calories. I discovered them after suffering through major leg cramps when I was training for my tris.