According to a first aspect, the invention relates to a container (10) for temporarily holding water on the roof of a building, including a bottom (11), a side wall (12) surrounding the bottom (11) and an overflow opening (14) for draining surplus water when the volume of water collected in the container (10) exceeds a buffer volume, characterised in that the container (10) includes a water-draining means configured to force water with a temporary storage volume which is lower than the buffer volume to flow according to a regulated leakage rate (13), and in that the dimensions of the bottom are smaller than the dimensions of a sloping roof on which the container (10) can be placed so that the water load is distributed evenly on the surface of the roof when a plurality of containers (10) of the same size cover the surface of the roof.
