永えい久きゅう硬こう水すい

noun

permanent hard water

Technical term in chemistry and water treatment; refers to water whose hardness cannot be removed by boiling, typically due to dissolved calcium and magnesium sulfates or chlorides.

• 永えい久きゅう硬こう水すいは煮しゃ沸ふつしても軟なん化かしない。

  Permanent hard water does not soften even when boiled.