Abstract: A water collection tray for vegetative and non-vegetative rooftop systems includes sidewalls, a bottom, and an open top that defines an interior region. A water separation barrier located in the interior region between the bottom and the top has multiple openings through which water admitted to the tray enters a water collector. A drain opening out of the tray from the water collector and in fluid communication with a water flow regulator causes all of the water flowing out of the drain to pass through the water flow regulator. Multiple water collection trays configured in an interlocking system provide for attenuation of rainfall to reduce peak flows of stormwater runoff from rooftops.