A hydrogen station is a storage or filling station for hydrogen.

Hydrogen storage is a term used for any of several methods for storing hydrogen for later use.

Hydrogen sulfide is the chemical compound with the formula H2S.

A hydrogen turboexpander-generator or generator loaded expander for hydrogen gas is an axial flow turbine or radial expander for energy recovery through which a high pressure hydrogen gas is expanded to produce work that is used to drive an electrical generator.

A hydrogen vehicle is a vehicle that uses hydrogen fuel for motive power.

Hydrogeology is the area of geology that deals with the distribution and movement of groundwater in the soil and rocks of the Earth's crust (commonly in aquifers).

A vessel equipped with hydrographic survey equipment to determine underwater topography in order to produce high-precision charts.

Hydrology is the scientific study of the movement, distribution, and management of water on Earth and other planets, including the water cycle, water resources, and environmental watershed sustainability.

Hydronics (hydro- meaning "water") is the use of liquid water or gaseous water (steam) or a water solution (usually glycol with water) as heat-transfer medium in heating and cooling systems.

Harnessing of water to produce energy.

A series of graphs drawn to a vertical scale of draught and a base of length, which gives values such as the centre of buoyancy, displacement, moment causing unit trim, and centre of flotation.

In fluid mechanics, hydrostatic equilibrium is the condition of a fluid or plastic solid at rest.

The pressure at any given point of a non-moving (static) fluid.

A part of the liferaft lashing used for automatic liferaft release. At up to 4m water pressure activates release mechanism and the liferaft is free to float clear to the surface.

Cargo tanks on oil tankers are loaded to 98% and in some cases 99% of capacity with the oil level well above the sea level.

Fluid statics or hydrostatics is the branch of fluid mechanics that studies "fluids at hydrostatic equilibrium and the pressure in a fluid or exerted by a fluid on an immersed body".

Hydrothermal circulation is the circulation of hot water.

Hydrothermal explosions occur when superheated water trapped below the surface of the earth rapidly converts from liquid to steam, violently disrupting the confining rock.

A hydrothermal spring is a spring produced by the emergence of geothermally heated groundwater that rises from the Earth's crust.

A hydrothermal vent is a fissure on the seafloor from which geothermally heated water discharges.