For centuries, falling water has been used in parts of the world to create energy to run grinding stones at mills and irrigation systems for crops. This interesting book shows how the use of this "clean" form of energy, called hydroelectricity, is being expanded to help us build a more sustainable future. Discover how other forms of water-based energy, such as energy from ocean waves and tides, are being harnessed and used to help create electricity to power our homes, offices, and factories.