A water wheel is a drive unit which runs on hydropower.
The book illustrates the entry with a photograph of a historic water-wheel installation: water pouring over a masonry dam drives a heavy timber shaft inside the mill — the kind of power source that drove wire-drawing works before the arrival of the steam engine.
See Also
Adapted from “"We do it straight" — Wire Straightening”, p. 195 (ISBN 3-00-005897-4).