The phrase 'Water under the Bridge' refers to past events to be put aside.
Example of use: "Sure, we have had our disagreements in the past, but that's water under the bridge now."
Interesting fact about Water under the Bridge
The origin of the idiom “water under the bridge” is an ancient one; this saying is derived from an even older one that dates back to ancient Greece. Heraclitus, a pre-Socratic philosopher who lived during the 4th and 5th centuries BCE, conveyed the same idea when he coined the phrase “You cannot step twice in the same river.”
