expression
a drop in the bucket; too little, too late; futile effort
Idiomatic expression meaning that a small effort or amount is completely inadequate to solve a large problem, like pouring water on a hot stone.
こんな少額の寄付では焼け石に水だ。
A donation this small is just a drop in the bucket.
Cleaning alone is a futile effort; it gets messy again right away.