A method and a plant for the treatment of water or wastewater having impurities by filtration of the water through two granular media filter stages of the moving bed type operated in series. The method includes the steps of feeding the water/wastewater as a first influent to first stage granular media filters; filtration of the first influent in the first stage granular media filters to produce a first effluent; feeding the first effluent as a second influent to second stage granular media filters; and filtration of the second influent in the second stage granular media filters to produce a second effluent. The second stage granular media filters are operated with intermittent washing of the granular filter media.