Video narration
Inside your small intestine, fluid contents are moving toward the colon-like water passing through a kitchen sponge. Normally, the intestinal wall steadily pulls water back into the body. As the contents travel through the small intestine and colon, they lose fluid and become more solid. Then the balance flips. An infection or toxin makes the wall release water and electrolytes-dissolved salts-into the gut. At the same time, normal water absorption drops. These two changes happen together. Fluid now builds up inside the intestine. The contents stay watery, and the intestinal muscles begin pushing them along more forcefully and quickly. That combination produces watery diarrhea. More fluid enters, less is taken back, and faster movement leaves less time for absorption. The watery stool is carried rapidly toward the rectum. This shows one general mechanism, not every possible cause.