The aim of this book is to propose a decision support tool for contractors before the execution stage to quantify the probability of risks in water supply system projects by using fuzzy logic incorporated with relative importance index (RII) method. Fifty one (51) different risk factors were identified through detailed literature review and interview with experts, and then categorized into seven (7) groups. The relative importance of risk factors were quantified by relative importance index (RII) method and the ranking of the factors and groups were demonstrated according to their importance...