Definition of water tube in US English:

water tube

noun

  • 1A pipe that contains or conveys water, especially any of those carrying water through a water-tube boiler.

  • 2Zoology (in invertebrates) a tubular structure that conveys water, such as a water vessel in an echinoderm or a vertical channel in the gill filament of a bivalve mollusc.

Origin

Early 18th century; earliest use found in John Desaguliers (1683–1744), natural philosopher and engineer.