1. INTRODUCTION
A water wheel is a system for extracting usable power from the water flowing in a river or stream.
There are 4 main types of water wheel. The first is undershot water wheel. It was shown in Fig. 1 (a). This
type is the oldest. Vitruv described the type of water wheel in the 1st century B.C. It can be used wherever
a swiftly running river is available. Its efficiency is around 25% in 19th century, this type of wheel was
further developed. Especially the design by Poncelet reached an efficiency of 70%.
The second is overshot water wheel. It was shown in Fig. 1 (b). Overshot water wheels are used since
the 14th century. If they are well-made and the height of the upper water reservoir allows a large diameter
of the wheel, an efficiency up to 75% or sometimes even 80% is possible.
The third is breastshot water wheel. It was shown in Fig. 1 (c). This is the most recent type, being
developed in 16th century. It is a compromise between the two basic constructions. Between the oldest
versions which had up to 45% efficiency and the modern types can reach up to 75% efficiency.