The term 'water-wheel' refers to a type of wheel that is powered by the flow of water. The most common type of water-wheel is the noria, which is a large wheel with buckets or compartments that fill with water and turn the wheel as the water flows out. A HELM is a smaller version of the noria, typically used for irrigation purposes. Finally, a sakieh is a type of water-wheel that is powered by the current of a river or stream, rather than the flow of water. All three types of water-wheels are used to generate power or to move water from one place to another.