A waterbar, also known as a waterstop, is a flexible strip typically made from PVC, rubber, or bentonite that is embedded in concrete joints to prevent the passage of water through the joint. It is commonly used in water-retaining structures like tanks, basements, tunnels, and reservoirs to create a watertight seal at construction or expansion joints. Waterbars play a crucial role in protecting concrete structures from water infiltration, thereby enhancing durability and preventing structural damage over time.