Water/hydro power is derived from the force or energy of moving water, which may be harnessed for useful purposes.

We have used running water as an energy source for thousands of years; in the early years this was mainly to grind corn. Cragside House, in Northumberland, England, in 1878 was the very first house to be lit by electricity produced by hydro power. Soon after, in 1882 on the Fox River, in the USA, there was enough water and power to generate sufficient electricity to light a house and two paper mills. Nowadays, there are many hydro power stations, producing around 20% of the world’s electricity.
 
Hydro energy is a renewable energy source as it follows the water cycle of evaporation, condensation and precipitation. As long as there is water, there will be an energy source.
Hydro power stations are usually constructed from a simple system design which has proven to be reliable over time. These are designed to last many years and can contribute to the production of electricity for many decades to come.
The main advantage of the hydro power system is the elimination of the cost of fuel. Once a dam is constructed, the hydro energy generated is virtually free. Hydro power stations are generally heavily automated and have few personnel on site during normal operation, therefore labour costs also tends to be low.
Hydro power is extremely efficient, is more reliable than wind, solar or wave power and electricity can be generated constantly.
If electricity is not needed at any time, the sluice gates can be shut to stop the generation of electricity. The build up of water in the lake means that energy can be stored above the dam ready to cope with peaks in demand, when the water is released to produce electricity. A great benefit is the ability for hydro-electric power stations to increase to full power very quickly, unlike other power stations.
Another main advantage is that hydro power is very clean. The dam systems do not produce any greenhouse gases, there is no waste and they do not pollute the atmosphere.  In addition they do not cause any noise pollution.
Micro-hydro systems are a miniature version of hydroelectric systems. These are ideal for remote sites where water is available a long distance from power needs.
A final benefit is that often large dams have become tourist attractions. The lake that forms behind the dam is ideal for leisure activities such as water sports.