硬水

1. Origins, structure, and basic meaning

• Structure: 硬水 (こうすい) is a noun for hard water, water with a relatively high mineral content.
• Basic usage: It describes the character of local tap water or a difference in tea brewed with that water.
  • この地域の水道水は硬水だ。 — The tap water in this area is hard.
  • 硬水で茶を入れると味の印象が変わった。 — Tea brewed with hard water tasted different from usual.

2. Common pitfalls and similar expressions

• Hard and soft water
  • 硬水 is mineral-rich hard water, while 軟水 is soft water with a comparatively lower mineral content.