Ground water is collected by drain rock and drain tile buried along the foundation (and, in some cases, under the floor). Drain tile carries the water to the sump tank (or two sump tanks, in a large house) that is buried in the basement floor.

The sump tank, also called a “basin,” “crock,” or “sump pit,” may be made of clay, tile, steel, concrete, fiberglass, or polyethylene. Though they vary in size, standard tanks are about 18 inches in diameter and 2 to 3 feet deep.

Normally, a sump tank is located at the lowest point in the basement. Most tanks have a hole in each side for incoming drain tile and all have a sturdy cover. When ground water fills the tank to a given level, a float or some other type of switching device activates a pump. (Though much less common, some pumps are controlled manually.) Many sump pump manufacturers sell polypropylene or fiberglass tanks custom-fitted to their pumps.

Why we like it: • Pump turns on if water rises in basement • Includes backup battery for when power goes out • Battery recharges automatically

Standard sump pumps are electric, powered by household current. There are two main types: submersible and pedestal. A submersible pump is completely concealed inside the tank. A pedestal model has a column that protrudes up through the tank’s cover; the motor is mounted on the column, above floor level.

Both types draw water in through a filter trap (this should be cleaned periodically). They pump water out through a discharge pipe and/or hose. As soon as an automatic pump empties the tank to a certain level, it’s motor turns off.

If the sump pump is connected to a sewer, the discharge pipe has a check valve and may have an anti-siphon device to prevent backflow. Or the discharge pipe may simply connect to a hose that carries the water well away from the house. Building codes in most areas dictate where the water must be discharged.