Hydro-power has a history going back at least 2000 years. The Doomsday book records 5000 waterwheels. One of the earliest hydroelectric schemes and ﬁrst in the world to power a private home was installed by the First Lord Armstrong in the 1880s at Cragside in Northumberland. This means, of course, that it is not exactly at the cutting edge of progress. The expansion of the National Grid sounded the death knell for many small-hydro schemes. However, it is increasingly now being perceived as an important source of clean electricity, devoid of the environmental penalties associated with large scale hydro-power. It has minimal impact on the environment resulting in almost zero emissions of sulphur dioxide, carbon dioxide and nitrous oxides. Nor does it cause acidiﬁcation of water; on the contrary it can oxygenate rivers and streams.