Oral rehydration therapy (also known as oral rehydration salts, or solution) is used to prevent and treat dehydration. Around the world, it is used to prevent serious illness and death from diarrhoea. It has been reported to reduce the risk of death by more than 90%. It is considered so important that it is a part of the World Health Organisation's list of essential medicines.
When you are losing fluid through sweat or diarrhoea, you are losing more than just water. You are losing important salts such as sodium. If you were to drink simply water, your body would lose most of it, and you would continue to lose the important salts at the same time. When taking O.R.S Hydration Tablets, the glucose helps get the sodium that is also included back into the body. This creates a path for water molecules to follow the sodium. It is a game of "follow the leader" back into the bodies cells, glucose first, then sodium, then water.