A drainage system for use in concrete masonry unit (CMU) wall construction comprises a tray unit of a size corresponding to size of CMUs, to be received beneath a course of CMUs, in use. The tray unit comprises opposite side flanges to abut a superjacent CMU and supporting a pan therebelow. The pan may be angled from back to front and from side edges to a middle portion thereof to urge water toward a front middle portion of the tray.