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