water under the bridge: 無法改變的事
He was relieved his time in jail was over and regarded it as water under the bridge.
他為服刑期滿而感到如釋重負，而且覺得既已無可更改，過去的就讓它過去吧。
Don't worry about that mistake, it's water under the bridge.
別擔心這個錯誤, 它已經無關緊要了.

check on: 查對，調查
Can I take a rain check on that?
我可以改日嗎？
Will you check on the time the train leaves?
請你核對一下火車開出的時間好 嗎 ?

no harm done: 一切平安無事
There, now, you're all right. No harm done.
好了，你現在沒事了，沒人受傷。
If I sulk for a few days, no harm is done.
如果我有那么幾天不高興, 沒有什么妨礙.