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.
nanopascals
The nanopascal is a multiple of the unit bit for Pressure. The prefix nano (symbol n) is defined in the International System of Units (SI) as a multiplier of 1.0 × 10-9 (1 billionth, short scale), and therefore 1 nanopascal = 1.0 × 10-9 pascals = 0.000000001 pascals. The nanopascal has the unit symbol nPa.