تعريف ومعنى "[spend] money like water"

What is the origin of the idiom "spend money like water" and when to use it?

The idiom "spend money like water" originates from the image of water flowing effortlessly and continuously, suggesting that money is spent freely and without hesitation, just as water flows without restriction. This phrase is used to describe someone who spends money extravagantly and without any thought to saving or conserving it.