Mankind has used water for centuries, but while those historical schemes made use of the derived mechanical energy to grind corn, for example, their modern counterparts usually generate electricity. Hydroelectric schemes are well known and already make a large contribution to the world's electricity supply. The total world resource for hydro, tidal and wave may be of the order of 6000 GW. Developments over the last 20 years have led to a number of concepts for wave energy converters which are technically feasible and are becoming economically attractive. Tidal power is of great interest in those locations with tidal ranges of 5-10 m. There are a few prototypes scattered across the world, the most famous being the La Rance scheme in France which has been operating since the 1960s. This article considers low head hydro schemes and reviews the current position of the related tidal and wave technologies, and concludes that the natural energy resources available should be exploited to provide a secure future.