The coastal regions, particularly deltaic regions, are the most developed and most densely populated regions all over the world. These regions are facing many hydrological problems both due to natural conditions and man's activities. The problems due to natural conditions range from flooding due to cyclones and wave surge to drinking fresh water scarcity due to problem of salt water intrusion. Man's activities compound these problems further. Salt water intrusion is one of the severe problems faced by coastal regions. Natural conditions and man's activities both contribute to this problem. There exists an urgent need to study systematically the causes and remedial measures for salt water intrusion problem in coastal areas. This report presents the hydrological aspects of salt water intrusion in coastal aquifers, salient features of Saturated-Unsaturated TRAnsport (SUTRA) model, and simulation of sea water intrusion in Nauru Island.