A bathtub is a large, waterproof container built into a bathroom where people sit or lie down to wash themselves. Most bathtubs are made of porcelain, fiberglass, or acrylic and are shaped to fit a person's body comfortably. You fill a bathtub with warm water, settle in, and use soap to get clean. Some people prefer quick showers, while others enjoy a long, relaxing soak in the tub.

Bathtubs became common in American homes during the early 1900s as cities built water and sewer systems. Before then, many families bathed in wooden washtubs or metal basins, heating water on the stove and pouring it in bucket by bucket. Having a bathtub with running water was once considered a luxury.

Today, when someone has a great idea while taking a bath, people sometimes call it a bathtub epiphany, inspired by the ancient Greek mathematician Archimedes, who supposedly shouted “Eureka!” after discovering an important principle while bathing.