Mechanical Water Use

Introduction

While water resources are valued for human health and for sustaining food production, the energy contained in moving water such as rivers or tides can also be harnessed to do work through mechanical devices, or to create energy in small scale or large scale hydropower schemes. Globally, 1.4 billion people lack access to electricity, with an additional 1 billion having only intermittent access (UNDP 2012). As running water is a resource that is globally available and renewable, harnessing its power for mechanical uses can improve livelihoods and increase working productivity even in rural or developing areas where no local electricity source is available.

How Does it Work?

Regardless of the technology used to use water for mechanical power, the principle of mechanical water use is the same: that the kinetic energy contained in flowing water can be harnessed and converted into mechanical energy in order to do work. The amount of energy that can be harvested depends on both the quantity of water flowing, and the velocity (speed) at which it flows.

There are many devices that can be implemented to use water for mechanical purposes. Some of the most important technologies are summarised below:

Water Wheels

Adapted from TRYENGINEERING (2011)

A water mill is a structure that uses a water wheel or turbine to drive a mechanical process. A water mill works by diverting water from a river or pond to a water wheel, usually along a channel or pipe. The water's force drives or pushes the blades of the wheel (or turbine), which then turns or rotates an axle that drives machinery that is attached to it to do work. This machinery performs a specific task, such as transporting water or milling flour. Waterwheels can either be horizontal or vertical with respect to water flow. Horizontal water wheels are simpler, but require high water velocities to work well. There are many types of water wheel. One type, called a noria (pictured right) is used to transport water from a running stream into a trough for local water supply.

Water Mills and Improved Water Mills

A water mill is a water wheel or turbine that is connected to a device that drives a mechanical process. Water mills can be used for such purposes as grinding flour or agricultural produce, cutting up materials such as pulp or timber, or metal shaping. Traditional water mills are made from a wheel or turbine with wooden blades that turn when water runs through. The turbine or wheel then turns a grinder shaft, which is connected to a grinding stone.

Recently, improved water mills have been designed which replace wooden blades with metal, cup-shaped blades. This modification has led to a doubling of efficiency and operational capacity by over 100%. Improved water mills have been successfully used as a cereal grinder, paddy huller, oil expeller, saw mill, as well as to produce electricity when coupled with an electric generator (GORKHALI 2010).

Tide Mills

Tide mills are made with a water wheel that is either placed across a tidal inlet or a section of an estuary made into a reservoir. Rising tides enter the mill pond through a one-way gate that closes automatically when the tide begins to fall. The stored water can then be used to turn a water wheel.

River Turbines

River turbines are turbines placed in a flowing river or canal, which are tethered to one side, and pump water to the shore. Output depends on river speed and depth.

Hydraulic Ram Pumps

Also known as “hydrams”, hydraulic rams are automatic pumping devices that use a large flow of falling water through a small head (low elevation) at an inlet in order to lift a small flow of water through a much higher head (high elevation) at an outlet, thus lifting the water (PRACTICAL ACTION 2002).

Applications of Mechanical Water Use

The dominant uses of mechanical power include water supply, agriculture, agro-processing, natural resource extraction, small-scale manufacturing, and lifting and crossing.

Water Supply

Having a clean and reliable source of drinking water is essential in improving the health of a community. In rural areas, water collection is often the responsibility of women, and consumes a great deal of time and energy. Mechanised water pumps can reduce the time and physical strain of water collection for women, allowing them to focus more on other activities, such as caring for children or taking care of their own health.

Agro-Processing

Post-harvest activity can be critical in helping farmers increase their income. For activities like milling, pressing, cutting, and shredding, Improved water mills can have an 80–90% increase in power use and efficiency compared to a traditional water mill. They can also have multiple uses such as for both agro-processing and power generation, which can increase the load of the mill and make such installations more sustainable.

Natural Resource Extraction

Artisanal and small-scale mining may be the only livelihood opportunity for some people, or may be their source of income during the agricultural off-season. There are many technologies that can reduce the effort needed for mining mentioned below.

Small-Scale Manufacturing

Mechanical power technologies allow micro-enterprises to produce goods consistently at the same quality and at a faster production rate. This, in turn, will directly affect their income for the same time spent on labour.

Lifting

Water can also be used for transport purposes. In countries such as Switzerland and France, water has historically been used for powering cable cars, using natural gradients and counter weights to drive cars up and down hills. These technologies are still in use today, but many have been replaced with designs that are powered by engines (DE DECKER 2009).

How to Optimise?

Mechanical water use is a non-consumptive water use. Therefore, there are possibilities to link mechanical water use to other uses, such as irrigation in agriculture. This can reduce the investment costs for individual users, thus expanding the possibilities for income generation and development.

Water for Energy and the Millennium Development Goals

Mechanical uses of water have many positive development impacts, which can be regarded for each of the Millennium Development Goals:

For more information on the Millennium Development Goals with regard to water and sanitation, see Access to Water and Sanitation, and Water Sanitation and Development.

Cost

• Because of the large increases in working productivity and efficiency, mechanical water use is considered to be one of the most cost-effective ways of supporting poor people.
• Mechanical devices are generally low-investment. However, the upfront capital needed is a key barrier in rural areas where investment capital is scarce. Microfinance institutions have been successful in overcoming this barrier.
• When investment capital is available, mechanical water use can nearly double revenue due to increased productivity.
• When multiple users are involved (for example when coupling mechanical water use with irrigation), investment costs are decreased for all users, and there may be greater opportunities for income generation.