Principle of Hydropower

A mass of water moving down a height difference contains energy. This can be harvested. Moving water drives some waterwheel/turbine. This rotation either drives machinery directly (e.g. mill, pump, hammer, thresher, ...) or is coupled with a generator which produces electric power.

Hydropower is probably the first form of automated power production which is not human/animal driven. Moving a grind stone for milling first, developed into the driving of an electrical generator. Next to steam it was for long the main power source for electricity.

Its continual availability does not require any power storage (unlike wind/solar power). It is mainly mechanical hardware. This makes it relative easy to understand and repair-/maintainable. In smaller units its environmental impact becomes neglect-able (see: environmental impact assessment and pros and cons of micro hydropower) .

In order to create electricity from hydropower, two parameters are critical:
Flow; or the minimum amount of water that is constantly available throughout the entire year
Head; the difference in height

These specific conditions limit generalising and standartisation of "how to install hydropower plants". Choosing the right location and planning requires some specific knowledge. With knowledge of water flow and height difference the potential power can be estimated.