In steam-boilers, a vertical water-space connecting other water-spaces, and crossing a flue-space, by which its contents are heated.(noun)
The Century Dictionary (Public Domain)
Use "water-leg" in a sentence
"Boilers utilizing water-leg construction are not ordinarily provided with mud drums."
"Repairs in water-leg boilers are difficult at best and frequently unsatisfactory when completed."
"Were such an explosion to occur, it would still be localized to a much larger extent than in the case of a water-leg boiler and the header construction thus almost absolutely localizes any danger from such a cause."