water under the bridge河流中的水源源不断流入大海，并非是静止不动的。在桥下流过的水也不会再回流。引申为已成往事，不可改变的既成事实，无法挽回的过去。

【例句】
He was relieved his time in jail was over and regarded it as water under the bridge.
皮卡丘对自己的刑期已满而感到如释重负，已把它当成往事不再挂怀。

All that is now just water under the bridge.
所有那些现在都是不可改变的事实了。