The invention relates to an installation for treating water by flotation, said installation comprising flotation equipment consisting of a flotation cell (10) into which flocculated raw water mixed with micro-bubbles produced by a pressurization-depressurization system (11) is guided, said cell being provided with a perforated collection device (13) designed in such a way that the surface of the flotation cell is crossed by an identical and uniform flow of water to be treated. The inventive installation comprises capture modules (14) which are arranged in the flotation cell in such a way that the lower part thereof is located at a distance (h) from the perforated collection device (13), said distance being determined such that any disturbance of the uniform distribution established by the perforated collection device is avoided.