How Do Water Powered Mills Work?

Water powered mills are mills and machinery that are powered by moving water. Flowing or falling water is used to create mechanical power that then performs tasks like grinding grains, pumping water, or powering textile mills. Water wheels or water turbines convert the energy of flowing or falling water into useful forms of power.

Water wheels were some of the earliest machines used for powering mills. The ancient Greeks used water wheels for grinding wheat into flour over 2,000 years ago. Water wheels were also widely used in the Roman Empire. During the Middle Ages, water wheels spread throughout Europe and helped drive the growth of various industries like milling and textiles. From the 1800s onward, water turbines began replacing water wheels as the main method of harnessing water power.

The two main types of water powered mills are those driven by water wheels and those driven by water turbines. Water wheels capture the energy of flowing water and are used on streams and rivers. Water turbines convert the energy of falling water and are often used in dams to generate hydroelectric power.

Water Wheels

Water wheels harness the energy of flowing or falling water. They convert the kinetic energy of water into rotational energy that can be used for various mechanical processes like milling grain or pumping water. There are two main types of water wheels: vertical wheels and horizontal wheels.

Vertical water wheels are the most common type. They have buckets or paddles mounted around the wheel’s circumference that catch flowing water. As the water fills the buckets, its weight causes the wheel to turn. There are three main types of vertical wheels based on where they get their water supply:

  • Overshot wheels – Water flows to the wheel from above, hitting the paddles at the top.
  • Breastshot wheels – Water enters the wheel at about halfway up its height.
  • Undershot wheels – Water flows underneath the wheel, hitting the paddles at the bottom.

Horizontal water wheels have a horizontal axle and are pushed by water flowing past them. They include undershot wheels placed directly in a river or stream as well as paddlewheels on boats.

The mechanics of water wheels involve converting the kinetic energy of flowing water into rotational kinetic energy. The weight of the water applies a torque force to the wheel, causing it to rotate. Overshot and breastshot wheels are generally more efficient since the water falls farther and impacts the wheel with greater force.[1]


Turbines are advanced water wheels that convert the energy of flowing water into rotational energy by directing water to hit buckets or blades attached to a wheel or rotor. Turbines are categorized as either impulse turbines or reaction turbines depending on how they extract energy from the water flow.1

Impulse turbines, like the Pelton and Turgo turbines, extract energy from the kinetic energy of a water jet that hits the buckets and changes direction. The water jet is created by directing the water flow through nozzles which increase the speed and pressure of the water. Impulse turbines allow water to exit without reducing pressure.

Reaction turbines like Francis, Kaplan, and Propeller turbines operate by water flowing through the turbine itself, reducing pressure by transferring kinetic energy to the rotor. The change in pressure or water pressure across the turbine provides the force to drive the rotor. Reaction turbines are suitable for lower heads and allow flexibility in regulation.

Major impulse turbine types:

  • Pelton – Split water jet hits cupped buckets along the wheel rim
  • Turgo – Jet hits angled blades on the rim of a runner

Major reaction turbine types:

  • Francis – Radial flow, runner blades form channels to guide water flow
  • Kaplan – Axial flow, adjustable wicket gate and rotor blades
  • Propeller – Axial flow, fixed blades shaped like ship propellers

Power Transmission

Water wheels convert the mechanical energy of falling or flowing water into rotational energy that can be used to power machinery. The power transmission system is responsible for transferring this rotational power from the water wheel shaft to the machinery being driven, such as millstones. This is accomplished through the use of gear trains and drive shafts.

Gear trains utilize gears of varying sizes to increase or decrease rotational speed and torque. Spur gears transfer power between parallel shafts while bevel gears transfer power between intersecting shafts. Worm gears can provide even higher gear reductions. The proper gear train must be selected based on the speed and torque requirements of the machinery being driven (1).

Drive shafts transfer rotational power from the gear train to the machinery. They are typically constructed of wood or steel and spin on bearings that allow smooth and efficient rotation. Bearings support the drive shaft while minimizing friction. Historic bearing designs utilized wood or leather while modern bearings employ ball bearings, roller bearings, fluid bearings, or magnetic bearings. Proper bearing selection and maintenance is critical to ensure long lasting and reliable power transmission (2).

By combining gear trains and drive shafts, the power from a water wheel can be smoothly and efficiently transmitted to power all manner of machinery in a mill.



Milling with Water Power

image of a water wheel used for milling grains

Water power has been harnessed for milling grains, sawing wood, and powering trip hammers and other industrial processes for centuries. Evidence shows water mills being used for industrial purposes as early as the 7th century in the Islamic world (Mutazilism and Arab astronomy, two bright stars in our …, n.d.). By the 11th century, water mills were widespread across the provinces of the Islamic empire (Sociopolitical and Cultural progress if Roman Empire survives, 2009).

One of the most common uses of water mills historically was for grinding grains like wheat, corn, rye and others into flour. The mechanical energy of a water wheel spinning an internal grindstone against a stationary stone allowed efficient milling of large quantities of grain. The first documented use of water mills for grinding grains dates back to the 1st century BCE in ancient Rome.

Sawing wood was another common application of water mill power. A water wheel could turn a belt drive connected to a saw blade to cut logs and lumber. Water-powered sawmills date back to Roman times and were widely used across Europe by the Middle Ages. The trip hammer was also an important industrial hammering device powered by water wheels and used for forging iron, fulling cloth, and other applications.

Modern Hydro Power

Modern hydroelectric power utilizes the energy of flowing water to generate electricity on both large and small scales. Three main types of modern hydroelectric systems are used today:1

Large Scale Hydroelectric Dams

Large dams are constructed on rivers to create reservoirs and control water flow. The water is released through the dam, flowing through turbines to generate electricity. Large scale hydroelectric dams can generate hundreds of megawatts of power and provide energy storage by pumping water back into the reservoir during times of low electricity demand. However, large dams also disrupt river ecosystems and can require relocating communities.

Run-of-River Systems

Run-of-river systems generate power from the natural flow of rivers, without the use of dams or reservoirs. These systems have a minimal environmental impact but generate less power than large dams. Run-of-river is well-suited to locations with steady water flow.

Micro Hydro Systems

Micro hydro systems generate under 100 kilowatts of electricity by diverting a portion of a river’s flow through a turbine. They provide localized power solutions with minimal environmental impact. Micro hydro can utilize existing infrastructure like irrigation canals or industrial water systems.


The efficiency of water wheels and water turbines depends on several factors. According to Testing and Performance Evaluation of Improved Water Mill (Improved Ghatta) Runners, the factors affecting water mill efficiency include the velocity of flow, design of buckets and blades, speed regulation, and inclination of the buckets (Source). Water wheels convert the kinetic energy of flowing water into rotational mechanical energy, so maximizing the velocity and volume of water flow is critical. The angle and curvature of the buckets or blades also impacts efficiency, as does the ability to regulate rotational speed as water flow changes. Properly designed water wheels can reach mechanical efficiencies of 60-80%.

In comparison to other power sources of the time, water mills offered much higher efficiency than human or animal labor. As noted in The Medieval Networks in East Central Europe: Commerce, Contacts and Communications, water mills greatly increased productivity for grinding grains over rotary hand mills (Source). Their continuous mechanical power was a major advancement for early industrial processes. However, water mills could only be built in suitable locations with fast flowing water. Modern hydroelectric turbines now convert water power into electricity with efficiencies exceeding 90%.

Environmental Impact

Water wheels and hydroelectric power can have both positive and negative impacts on the environment. On the positive side, hydropower is a renewable energy source that does not emit greenhouse gases or other pollutants. As noted by the Attleboro Public Library, “The environment is not harmed by pollution, unlike with the burning of coal or natural gas” ( This makes water wheels and hydroelectric dams a low carbon way to generate electricity.

However, dams and water wheels can also have negative ecological effects. As ScienceDirect notes, “Often, building of dams disturbs the natural environment, creates flooding of land, destroys the natural habitat of animals and even people, and leads to water quality problems” ( One major concern is that dams can prevent fish migration and movement upstream. To mitigate this, fish ladders are often constructed to allow fish to bypass dams and water wheels. Overall, hydropower provides clean renewable energy but steps must be taken to minimize disruption to river ecology and habitats.

Notable Examples

Some of the most notable historical examples of water powered mills include the Slater Mill in Pawtucket, Rhode Island and the Old Mill at Tuckahoe in New Jersey. The Slater Mill was the first successful cotton spinning mill in America, founded in 1793 by Samuel Slater. It ushered in the American Industrial Revolution and is now a museum showcasing the history of industrialization in America. The Old Mill at Tuckahoe is an example of early American gristmill architecture that dates back to 1698. It is one of the oldest continuously operating mills in the United States and serves as a living monument to America’s agricultural and industrial heritage.

These mills showcase early American industrial architecture and technology. They provide insight into America’s shift towards industrial manufacturing and serve as important monuments for understanding the country’s history. Their preservation allows visitors to experience and learn about America’s Industrial Revolution first-hand through guided tours, exhibits, and demonstrations. They are prime destinations for those interested in industrial archeology to see water powered mills that played a pivotal role in early American industry.



Water mills have had an enormous impact and lasting legacy throughout history. As evidenced in sources like Munro’s “Industrial energy from water-mills in the European economies” (1) and Igliński’s “Hydro energy in Poland: the history, current state, potential” (2), water mills revolutionized manufacturing and economic development starting in ancient times. Their simple yet ingenious use of flowing water as a power source enabled massive increases in productivity across countless industries from textiles to metals.

Even with the advent of steam power and electricity, water mills continued to play an integral role in many local economies up through the 20th century. Today, the principles of hydropower live on in modern hydroelectric dams and smaller scale installations that provide renewable electricity around the world. Water mills paved the way for humankind’s ability to harness the energy of moving water, which remains an indispensable part of our energy infrastructure.

The innovative engineering of water mills has stood the test of time. Their legacy will continue, as new generations tap into the potential of hydropower in ways that build upon the foundations laid centuries ago by our water milling ancestors.

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