In this paper, the operation of mono and dual media filter beds was examined in a large-scale drinking water treatment plant, located in Thessaloniki (N. Greece). The efficiency of filtration process was improved, regarding the removal of undesirable constituents, which mainly include organic matter and suspended solids (turbidity). A comparison was attempted between a sand filter bed (of 1 m depth) and a dual media filter bed, consisting of sand (60 cm-bottom) and anthracite (40 cm-top) layers. Two alternative treatment schemes were examined: the conventional coagulation-flocculation/sedimentation, followed by gravity filtration and the direct filtration (i.e. coagulation-flocculation and filtration, but without sedimentation). All these experiments were conducted at fullscale filter beds, presenting an effective surface area of 40 m(2) and with a volume loading rate over 375 m(2) V (i.e. large-scale experiments); therefore, the respective velocity was around 10 m V. The performance of filter beds was assessed in terms of removal capacity, regarding mainly the turbidity, as well as the head-loss build-up. It was found that the dual media filter bed produced water of the same (high) quality as the single bed, but with the advantage of operating at greater filtration cycles (around 3 times higher), which resulted to a 10% higher water production.