Problem of supplying the population with drinking water of high quality assume ever-greater importance because of development of an environment, which is polluted by industrial waste products. The substances, which are now found in surface & ground water, vary in different world region because of many factors. These factors are the type of agricultural & industrial processes in water accumulated area, the quantity & quality of water treatment processes, pretreatment technologies of drinking water and waste water purification. The level of contamination of water sources is so high that water can no longer be considered as a harmless natural product; it depends on special treatment & control. In this thesis, a computer model is designed for various units of conventional water treatment plant. These units include primary sedimentation tank, coagulation & flocculation tank, secondary sedimentation tank, slow sand filter &rapid sand filters. The basic aim of undertaking this research is to develop a computer program, which will help to analyze, design, & manage different units of water treatment plant effectively and optimize them. This computer model named water Treatment Designer is developed in Visual Basics for application, which help in designing of different units of conventional water treatment plant. The design is easy to understand & applicable to solve problems related to environmental engineering disciplines. The model is run for different parameters used in water treatment process. The complete design steps & formulas have been presented in organize form in this thesis. This model will help undergraduate students, graduate students & the technical staff working in water supply & sanitation schemes to know about the basic water treatment plant processes. This paper was presented in INTERNATIONAL CONFERENCE ON ADVANCED MODELING & SIMULATION – ICAMS 2011 http://www.nust.edu.pk/INSTITUTIONS/Colleges/CEME/Departments/Mechanical%20Engineering/Events/Pages/ICAMS-2011.aspx