Wiktionary
watertightness
n. (context rare English) The condition of being watertight
Usage examples of "watertightness".
They began checking the rigging, the bicycle frames, and even the watertightness of the boatframe and the balloons.
The secondary receptacle was then capped, taped for watertightness, labeled with the name, address, and phone number of the sender at San Jose Mercy, and encased in an outer shipping canister.