A method and a plant for the treatment of water or wastewater, having impurities therein by filtration through two granular media filter stages (1, 2) of the moving bed type operated in series, comprising: feeding of said water/wastewater as a first influent to first stage granular media filters; filtration of said first influent in said first stage granular media filters to produce a first effluent; feeding said first effluent as a second influent to second stage granular media filters; and filtration of said second influent in said second stage granular media filters to produce a second effluent; wherein said second stage granular media filters (2) are operated with intermittent washing of the granular filter media.