water under the bridge

過ぎてしまった事、取り返しのつかない過去

Ex

  • That’s all water under the bridge.
  • It’s water under the bridge. You have to move forward.

Reference source

  • https://ejje.weblio.jp/content/water+under+the+bridge
  • http://www.beo.co.jp/atoz/english/water-under-the-bridge.html