It is an edible and medicinal plant, one of the oldest plants in the world.

An excerpt from the article 20 facts about watercress

Its health-promoting properties have been known since ancient times. The Egyptians served workers the juice of fresh watercress in the belief that it would increase their productivity at work. The ancient Greeks were convinced that watercress increased intellectual abilities. It was also valued by Napoleon. It was also an ingredient in the menu prepared for Prince William's wedding to Duchess Kate at Buckingham Palace (it was served as an ingredient in a tart - asparagus with watercress).