The primary function of the colon is to absorb water and electrolytes from the chyme delivered and determine the frequency, consistency, and volume of stools eliminated. The colon mixes luminal contents so that they are optimally exposed to the absorptive mucosal surface; slowly propels feces caudally to allow adequate time for the absorption of water, electrolytes, and metabolic products of bacterial degradation; allows storage of feces; and rapidly and efficiently propels during defecation. Transit time through the colon is significantly slower than through the proximal bowel and is achieved through contractions that are less coordinated.

So the colon plays a beneficial role in maintenance of overall potassium homeostasis. The intestine possesses a tremendous capacity to absorb water. About 7-10 liters of water entering the gastrointestinal tract during a 24 hour period is absorbed by the small intestine.

The colon also plays an effective role in the desiccation of bowel by absorbing an additional 2 liters of fluid. Several conditions causing malabsorption of solutes and water in the small intestine can increase the fluid entering the colon to overwhelm its absorptive capacity and hence lead to diarrhea.