water column

noun4

1. •
   A notional column of water from the surface to the bottom in a natural setting, notable for the differences in physical and chemical properties at various depths.
2. •
   The zone in which ascent and descent occur.
3. •
   The column of water inside the graduated cylinder of a pressure gauge that measures pressure in inches of water.
4. •
   A column alongside a railway track used to replenish a steam engine's water supply.

   • At Carlisle, as is customary, there was a very slow stop for the engine to draw to the water column. — 1943