The colon plays a major role in reabsorbtion of water and electrolytes. When the colon is excised and the patient has an end ileostomy then there is usaully no problem. However, if there has been a major loss of small bowel in addition then the patient may have enough small bowel to absorb calories but insufficient to guarantee fluid balance. A length of small bowel emptying via a stoma may lead to fluid and electrolyte loss but if this is connected to a moderate length of healthy colon then the colon may absorb sufficient fluid to prevent fluid and electrolye loss.
The small bowel absorbs 80%, or all but 1.5 to 2 liters, of the 8-10 litres of fluid entering the gastrointestinal tract. The colon then absorbs 90% of this fluid, leaving 0.1 liters of water in a normal bowel movement.