fluid reabsorption is isotonic
1 A large amount of fluid is cycled through the bowel each day. ( 2 net reabsorption = 98%) Intestinal fluids are isotonic. 3  Water is reabsorbed passively down its osmotic gradient created by the active reabsorption of nutrients and electrolytes.bout 1500 mls/day enter the colon from the ileum. This means that over a litre per day is absorbed in the colon. The intestinal contents are essentially isotonic by the time the jejunum is reached because water can move into or out of the intestine in response to any osmotic gradient.