I weigh about 190 pounds. That's equal to about 85 kilograms.
To figure out the appropriate hourly fluid replenishment for a (basically) healthy 85 kg patient just lounging around in the hospital we follow the 4-2-1 rule, which is that for the first 10 kg we supply 4 cc per kg per hour, the next 10 is 2 cc per kg per hour and then 1 cc per kg per hour for the rest of the weight. So 40 + 20 + 65 = 125 cc per hour.
This means that a basically healthy 85 kg guy (like me) loses around 125 mL of fluid from urine and insensible losses (think sweating, respiration, etc) per hour.
Over a 25 hour period that amounts to a nice figure of 3,125 mL or 3.125 Liters. Think about it - that's a huge water debt. A big bottle of soda is only 2 Liters of fluid.
People don't drink enough before a fast and it's dehydration far more than hunger that makes them feel like crap.
So drink well and have a meaningful fast.