Watermills are mills that use the force of moving water to operate their internal mechanisms. The hydropower comes from the force of the water turning a waterwheel placed in its’ path. As such, watermills must be located on a stream, river, or source of moving water. Watermills may be sawmills, gristmills, papermills, textile mills, or another type of mill. They can be designed to saw, roll, grind, or hammer continuously.

There are two main types of watermills (though other types do exist):

• Undershot: The waterwheel is placed directly in a stream or river and is turned by water moving underneath it.
• Overshot: Water is diverted via a small aqueduct or channel and poured over the top of the waterwheel in order to turn it.

If your world has fictional materials, fictional plants, or other resources, consider if watermills may be used in the production or refinement of this resource.

The first watermill dates to between 40-10 BC.