Pumping

Though abundant globally, water is often out of reach. When water is far away, energy is used to transport it. And, because of its density—water weighs 1,000 kg/m³ (8.34 pounds per gallon)—the energy required to raise water is significant. The total energy needed for pumping water depends on the height to which the water is raised, the rate at which it is raised, pipe diameter, friction, and other factors. Whether raising water from a well or pumping water over a mountain, the total energy required must overcome the force of gravity exerted on that volume of water.

The ancient Egyptians used Archimedes’ screw, which is a clever device that converts the manual turning of a screw into a process that elevates water. The tight coil of connected blades raises water as long as it is continually operated. Its invention is attributed to Archimedes in the third century BCE, but might have been in use earlier. Thousands of years later, modern water-lifting stations at amusement parks, water treatment plants, and elsewhere still make use of the design.

A medium-sized U.S. city with one million residents might need 570 million liters (150 million gallons) of water per day. Raising that water from surface sources to elevated water treatment plants over a height of 100 meters requires a little more than 6 megawatts (MW) of pumping power. Massive wind turbines generate approximately 1 MW each, so the city would need 6 turbines running at full capacity exclusively for pumping water to the treatment and storage facility at the top of the hill, after which it can flow downhill to customers. The energy intensity of pumping is one of the reasons why people prefer shallow wells and surface water sources. Deeper, dirtier sources require even more energy and are usually only deployed when less energy-intensive options are available.

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