A flat surface for sinks and shower pans with drainage through channels, which, as a single component, has a flat upper surface (1) in which interconnected radial and peripheral channels (2) are made, which guide the water to a drain (3) arranged in the lower part thereof, and partial grooves (4) run between the channels (2), said grooves having a recess to prevent the water from spilling over, and this upper flat surface (1) is arranged over a concave water collection tray (5) which leads into the drain (3).