Illness puts a greater demand on your body for resources, which in turn can dehydrate you more quickly. Staying hydrated can be especially difficult when you are feeling nauseas or experiencing vomiting and/or diarrhea.
Plain water does not contain electrolytes which are essential to properly function muscles, balance the PH of your blood and more. Electrolytes are naturally lost when you sweat. Your body does not produce electrolytes on its own, so these minerals must be replaced daily by ingesting food, beverages, supplements, and even IV Fluid Hydration.