Abstract: 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. A strip of water permeable material is attached to an upper surface of the pan and extends transversely beyond a front edge of the pan. A block of water permeable material is positioned above the pan and extends upwardly into a hollow core of a CMU. The water permeable material of the strip and the block has a porosity sufficient to permit water to pass there through but substantially insufficient to permit mortar and debris to pass there through so that water in a hollow core of a CMU drains through the strip.