What It Is and Why You Might Need It The human body needs water to function. When it doesn’t get enough, it sends out signals letting you know you’d better give it some fluids. and soon. Although you might be tempted to start chugging water or a sports drink when you feel like your body is low on fluids, that’s not always the best option. It can take hours for the body to rehydrate when drinking fluids because your large intestine absorbs most of the fluid. Drinking large quantities of fluids quickly may also cause issues as bothersome as the dehydration that sent you drinking in the first place.