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seawater; saltwater
海水が冷たくて気持ちいい。
The seawater is cold and refreshing.
この浜辺は海水がとても澄んでいる。
The seawater at this beach is very clear.
海水を蒸発させて塩を作る方法は古くから知られている。
The method of making salt by evaporating seawater has been known since ancient times.