this is a very good thread. I just wanted to say that day by day our needs are different. I had to fast for a dr's appt and by the time they looked at me my bp was 80 over 50 and she was pretty freaked out about it. She says that a lot of us are always borderline dehydrated and that for a ride I should start hydrating the night before. Now a year ago I did tour de blast and was still thirsty (and drinking lots) 3 days later.. Last week I did another mountain pass ride and followed Dr's instructions. My husband was very annoyed (I drank some of his water) but I was rehydrated the next day and quite pleased with myself. I'm not drinking enough to swamp myself, but really, any symptoms like cramps or headaches are better tackled immediately.