noun
Used as a noun in Japanese, often in technical or product contexts to describe something that does not let water in or out.
このケースはウォータータイトで、雨の日でも安心です。
This case is watertight, so you can feel safe even on rainy days.
防水 is the common native Japanese term for waterproof or water-resistant, while ウォータータイト is a more technical English loanword often used in product specifications.
Loanword from English 'watertight'.