淡水(たんすい)

WORD FORMATION:
淡(たん) (light, pale, dilute) + 水(すい) (water). Literally "light water" — water with low salt content.

REGISTER:
A formal/scientific term. In everyday speech, people are more likely to describe water as 塩分(えんぶん)のない水(みず) (water without salt).

COMMON COLLOCATIONS:

• 淡水(たんすい)魚(ぎょ): freshwater fish
• 淡水(たんすい)湖(こ): freshwater lake
• 淡水(たんすい)生物(せいぶつ): freshwater organisms
• 淡水(たんすい)資源(しげん): freshwater resources

CONTRAST:

• 淡水(たんすい): fresh water (not salty)
• 海水(かいすい): sea water
• 塩水(えんすい): salt water
• 汽水(きすい): brackish water (mix of fresh and salt)