If you put your hand under the kitchen tap or stick your toe into a fast-flowing river, you can feel the push of the water. Water has great power. This is something that the ancient Greek hero Hercules knew only too well. He used the strength of water to clean the stables of King Augeas. They were so dirty that no human being had the strength to scour them. But Hercules diverted a river toward the stables, so that its strong flow washed away all the dirt.

Through the centuries engineers have built machines capable of harnessing the power of water and converting it into mechanical energy. Like Hercules, their challenge has been to use water to perform laborious tasks and to make our lives easier.

In ancient times, flour was made by hand. This was very tiring. Laborers placed the grain on a flat stone and then used another stone, or perhaps a stone pestle, to pound the grain into flour. However, in ancient China, Egypt and Persia, inventors found a way to make the work easier. They built machines called waterwheels to grind grain, such as wheat and corn, into flour.