In construction, a waterbar, or more commonly a waterstop, is a flexible barrier installed at concrete joints to prevent water leakage and maintain watertightness. Made from materials like PVC or rubber, waterbars are embedded into concrete structures to form a continuous seal against water infiltration through construction, expansion, or control joints. They are essential for structures like basements, tunnels, and reservoirs to enhance durability and longevity by accommodating movement and preventing costly water damage.