Le mot du jour : “Mettre de l’eau dans son vin”
“Mettre de l’eau dans son vin” is to pour water in your wine, to water it down. That expression goes back at least as far as the 16th century.
At the beginning, it just meant to mix up some water in the wine to make it less strong.
But with time, the meaning changed, and now you use it when you talk about being more moderate.
Ex : “Il est trop têtu, il devrait mettre de l’eau dans son vin” (he is too stubborn, he should tone it down)
As for actually putting water in your wine, it’s not very well considered (at least in my family, where it would be seen as a sacrilege), except if the wine tastes really bad 😉