Let’s break down what occurs once you drink salt water: Salt is sodium and chloride, that are electrolytes that exist already in your blood and hold onto water, says Gina Sam, MD, MPH, a gastroenterologist in New York Metropolis. While you drink salt water, the surplus sodium and chloride primarily pull water into your colon, stimulating a bowel motion. In reality, many laxatives that medical doctors prescribe to prepare for a colonoscopy are salt-based for this very purpose, she says. “So primarily, what you are doing is not one thing fancy, you are mainly doing a laxative,” she says.