A centimetre of water (US spelling centimeter of water, abbreviated cm H2O or cm H2O) is a less commonly used unit of pressure derived from pressure head calculations using metrology. It is frequently used to measure the central venous pressure, the intracranial pressure while sampling cerebrospinal fluid, as well as determining pressures during mechanical ventilation or in water supply networks (then usually in metres water column). It is also a common unit of pressure in the speech sciences. {|