Most Australians, whatever microclimate they live in, know the importance of hydration, especially cyclists, who often exercise for extended periods. Yet each summer, many are hospitalised due to simply not drinking enough fluids. Dehydration is not just feeling thirsty. It occurs when the body reaches a dangerously low level of water content, often caused by a sustained net loss of fluid. One third of our body is made up of water, and within our muscles the level rises to 75%.