What it means
Said when you’re ready to let go of a past argument or screw-up and stop dragging it into today. The idea is simple: the water’s already flowed on, so there’s nothing to stand on and fight about anymore. It can be genuine forgiveness or just a polite way of saying, drop it and move forward.
Usage examples
"I know I bailed on your birthday, but it’s water under the bridge now. Come on, let’s grab a drink and move on."
"We had a massive falling out years ago, but it is all water under the bridge now, we laugh about it these days."
"Sure he forgot my birthday once, but that is water under the bridge, he has made up for it tenfold since."
"Yeah, we had words last week, but it's water under the bridge now. No point carrying that mess into Friday."
"Mum was fuming when I dented the car, but it's water under the bridge now. She only brings it up for a laugh."
Where it comes from
It’s an old English idiom built on a very plain image: once water’s passed under a bridge, it’s gone and you can’t pull it back. That figurative sense was already in use by the early 1900s, and it stuck because it neatly says the past is past, whether you mean real forgiveness or just let’s quit rehashing it.
