Water level, also known as gauge height or stage, is the elevation of the free surface of a sea, stream, lake or reservoir relative to a specified vertical datum.

Water heating is a heat transfer process that uses an energy source to heat water above its initial temperature.

The water cycle, also known as the hydrologic cycle or the hydrological cycle, describes the continuous movement of water on, above and below the surface of the Earth.

Hydraulic shock (water hammer or fluid hammer) is a pressure surge or wave caused when a fluid, usually a liquid but sometimes also a gas, in motion is forced to stop or change direction suddenly.

Water cooling is a method of heat removal from components and industrial equipment.

Water is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms.

A wastegate is a valve that controls the flow of exhaust gases to the turbine wheel in a turbocharged engine system.

Waste-to-energy plants burn solid waste, often called garbage or trash, to produce steam in a boiler that is used to generate electricity.

A heat exchanger used to transfer energy from one source to another.

Cogging torque of electrical motors is the torque due to the interaction between the permanent magnets of the rotor and the stator slots of a Permanent Magnet (PM) machine.

A system that generates electricity and by collection of waste energy in that process can produce other energy resources, ie hot water or steam generated from the heat recovered from the engine exhaust system.

A ratio of useful heating (or cooling) to provide work. Higher COP's indicate higher efficiency.

In the cocurrent flow exchange mechanism, the two fluids flow in the same direction.

The Cockcroft–Walton (CW) generator, or multiplier, is an electric circuit that generates a high DC voltage from a low-voltage AC or pulsing DC input.

A tube in tube heat exchanger where water (or brine) is separated from refrigerant.

Coastal reservoirs are fresh water storage reservoirs located on the sea coast near the river mouth to store the flood water of a river.

The conversion of dead vegetation into coal is called coalification.

A coal-fired power station or coal power plant is a thermal power station which burns coal to generate electricity.

Coal pollution mitigation, sometimes called clean coal, is a series of systems and technologies that seek to mitigate the health and environmental impact of coal; in particular air pollution from coal-fired power stations, and from coal burnt by heavy industry.

Coal phase-out means stopping burning coal for energy, and is part of fossil fuel phase-out.