In this study four water quantity and quality problems are studied using advanced simulation and optimization techniques. This study is divided in two parts, the first part deals with water quantity management problems whereas the second part deals with water quality management problems. In the first part, two water quantity management problems are studied that include prediction of discharge in rivers and groundwater level predictions. In the second part of the study, two water quality management problems are studied, that include cost estimation of in-situ bioremediation and modeling of saltwater intrusion in coastal aquifer.