Chronic diarrhea commonly causes hypokalemia. However, life-threatening hypokalemia due to chronic diarrhea has not been reported in the adult caused by chronic ingestion of a fructose beverage. We report an adult patient who had severe hypokalemia from chronic osmotic diarrhea as a result of drinking 4 to 6 liters of Big Red daily for several months. This resulted in sustained hypokalemia, complicated by hypokalemic nephropathy and subsequent nephrogenic diabetes insipidus. All abnormalities cleared with potassium replacement, salt restriction, modest thiazide treatment, and abstinence from Big Red.