Operation and maintenance of the water treatment plants is not given the necessary importance in developing countries. In this literature, Dynamic Programming algorithm for functional design of water treatment system was developed. This study deals with the use of sensitivity analysis in maintenance of water treatment plant. Sensitivity Analysis is the study of how the variation in the output of a model can be apportioned to different sources of input parameters. A medium size water treatment plant with a capacity of 27.5 million litres per day was considered for case study. Sensitivity coefficients were calculated for different output parameters (diameter of floc particle, effluent suspended solids concentration and Head loss in filters) by effecting changes in the input design parameters (influent particle concentration, velocity gradient, surface overflow rate; filter run time and filtration rate). The input parameters and corresponding output parameters were analyzed to arrive at the sensitive parameters. Crucial parameters in a complex water treatment system is identified using the technique of Sensitivity Analysis.