noun
knowing how to swim
Refers to the ability or knowledge of swimming. Often used in contexts where one's swimming ability is relevant.
彼は水心があるので、海でも安心だ。
He knows how to swim, so he's safe even in the ocean.
Proverbial expression, abbreviated from 魚心あれば水心. Implies mutual goodwill or reciprocal favors.
See also: 魚心あれば水心
「水心あれば魚心」ということわざがある。
There is a proverb: 'If the water has a mind, the fish have a mind too' (kindness begets kindness).