watershed

Imagine rain falling on hills and fields around you. Every drop runs somewhere - into a stream, a river, a lake, or the sea. In common use, a watershed is the area of land that gathers that water and sends it to the same place. In some varieties of English, it can also mean the high line of land that separates one drainage area from another. But "watershed" is not only about geography. It can also mean a turning point in history or in someone's life - a moment after which things change in a clear and lasting way. You might say that the invention of the printing press was a watershed moment in communication.

The word "watershed" has a literal meaning and a figurative one. In everyday North American English, a watershed is usually the whole area of land from which rain and streams flow into the same river, lake, or other body of water. If chemicals, soil, or trash enter the water high up in that area, the effects can spread throughout the whole system downstream. That is why people talk about protecting forests, farms, and towns within a watershed. For example: "Protecting the forests in this watershed is vital for clean drinking water."

In some other varieties of English, especially British English, "watershed" can mean the line of high land that separates water flowing in different directions. This is close to what is often called a "drainage divide" or "water divide." The two senses are related: one focuses on the whole drainage area, and the other focuses on the boundary between drainage areas.

Figuratively, a watershed is a turning point - a moment that marks an important and lasting change. A watershed moment is not just any event; it changes what happens next in a serious way. For example: "The Supreme Court decision was a watershed moment for LGBTQ+ rights." You may also hear phrases like "a watershed year" or "a watershed event." In all of these uses, the idea is the same: after that point, the course of things is different.