My rule is 1 bottle an hour alternating GU20 (like Gatorade) and water when it's hot. When it's not hot, 1 bottle of GU20 every 2 hours. Having a hydration plan prevents over and under hydration.

For my century I tried pre-hydrating the day before, and I think it helped.

I found when I had the Camel back I drank constantly and had the Pee issue too.