expression, noun
bubble on the surface of water
Literal meaning: a bubble floating on water. Used descriptively, not idiomatically.
池の水面に水の泡が浮かんでいる。
Bubbles are floating on the surface of the pond.
expression, noun
Idiomatic use: efforts, plans, or hopes that vanish without result, like a bubble bursting. Often used in the pattern 水の泡になる (come to nothing). Sense 3 (something short-lived) is a less common extension of this metaphor.
長年の努力が水の泡になった。
Years of effort came to nothing.
彼の夢は一瞬で水の泡と消えた。
His dream vanished in an instant like a bubble.