Floc filtration and adsorptive filtration are the two main physicochemical mechanisms of iron removal in filters. Under the commonly applied treatment conditions in iron removal plants, the floc filtration is commonly believed to be the dominant mechanism and the adsorptive filtration complimentary. Iron removal filters with iron oxide coated sand are expected to perform better in terms of filtrate quality, filter run time and costs, by switching the mode of operation from predominantly floc filtration to predominantly adsorptive filtration. A decision support system (DSS) is being developed to assess the applicability and to quantify the possible benefits associated with adsorptive iron removal for a given groundwater and a specific plant. This paper introduces the different independent and interconnected modules of the DSS and elaborates on one particular sub-module for the analysis of the extent of floc filtration and adsorptive filtration iron removal in a groundwater treatment plant under given conditions. This computer model would be helpful in optimising the plant performance under the existing mode of operation, formulating strategies for switching from floc filtration to adsorptive filtration, and designing new iron removal plants. Sensitivity analysis showed that pH, iron oxidation rate constant and pre-oxidation time (a function of depth of supernatant and filtration rate) are the main parameters determining the extent of floc filtration and adsorptive iron removal under given conditions. Predominantly adsorptive iron removal in filters can be achieved by reducing the depth of supernatant, increasing the rate of filtration and/or controlling the oxygen concentration in the feed water.