What Is a Sump Pit and How Does It Work?

When people talk about a “sump pump,” they often mean the entire setup—but there’s a difference between the sump pit and the sump pump itself. Both work together as part of a larger drainage system, and both are key in preventing water damage in your basement or crawl space.

Sump Pit

A sump pit—sometimes called a sump pump pit or basement sump pit—is a hole dug into the lowest part of your basement floor or crawl space. It’s designed to collect excess water before it can cause flooding or foundation problems. During installation, a contractor digs a hole large enough to hold a sump basin, which is typically surrounded by gravel and filter fabric to let water flow in while keeping sediment and organic matter out. The hollowed-out area may be lined with brick, concrete, or a pre-molded sump pit liner.

Around the pit, a network of drain tiles or drain pipes directs water from the surrounding soil into the basin. The pit holds this water until it rises to a certain level, triggering the sump pump to remove it. A sump pit that is installed in the floor of a finished basement is usually covered by an ornate grate to obscure it from view.

Think of the sump pit as the “catcher’s mitt” of your drainage system—gathering groundwater, rainwater, and other naturally collected water from around your home’s foundation. Without it, your basement floor or crawlspace could easily become saturated during heavy rains or when the water table rises.

Sump Pump

The sump pump is the mechanical part of the system that removes the water. It sits inside the sump pit and is connected to a storm drain or municipal sewer system. A float on the sump pump automatically turns on the pump when the water level rises to a certain point. The pump then directs water up and out through a discharge line—a pipe that carries the water safely away from your house.

Most sump pumps include a check valve that prevents water from flowing back into the pit after the pump shuts off. When everything’s working correctly, the sump pump system moves water out before it ever reaches your floor surface. However, if the discharge line becomes clogged, blocked, or breaks, or if the pump fails, water can back up and lead to flooding, water intrusion, or foundation issues.

Basically, the sump pit collects the water; the sump pump removes it. Together, they protect your home from water damage, especially during heavy rains or when the water table rises close to your foundation.