A swimming pool, swimming bath, wading pool, or simply a pool, is a container filled with water intended for swimming or water-based recreation. There are many standard sizes; the largest and deepest is the Olympic-size swimming pool.[citation needed] A pool can be built either above or in the ground, and from materials such as concrete (also known as gunite), metal, plastic or fiberglass. The innovation of a composite construction of fibreglass, with an epoxy coating and porcelain ceramic tiles has led to the Pre-form, Composite-type with significant advantages over older methods; however, it also has increased sensitivity to metal staining.