In reply to a message regarding my 50 Euro fine by Trenitalia for not validating an 11 Euro train ticket from Rome's Airport, Leonardo da Vinci Airport or Fiumicino, I replied it was "Water under the Bridge".

In an overseas telephone conversation to a non British person, I was asked what did I mean by this English saying.

It means that something has happened, but it has finished and is no longer important.

So I was fined 50 Euro by Trenitalia, but it happened, there is nothing I can do about it now, so I can let any bad thoughts go, it is no longer worth thinking about.

Usage examples:-

I was once very close with a person, we argued and refused to talk to each other for a long time, but that is water under the bridge, and we became friends again and talk all the time.

I was married once, but the marriage failed and we divorced, so that time of my life is water under the bridge.