The 26, December 2004 tsunami had major impact on the quality of groundwater along the south- east coast of India, but especially in the tsunami-affected areas of the Nagapatinam district of Tamilnadu. Major pollution resulted primarily from increases in the salinity of groundwater. The post- tsunami water quality posed problems to general health and contributed significantly to agricultural and environmental degradation in the Sirkazhi taluk and Nagapattinam districts. The adverse impact was particularly significant in the areas of Pazaiyar, Madavaimedu, Thirumullaivasal, Thoduvai, Koozaiyar, Puthupattinam, Kizhamoovarkarai, Poombhukar and Vanagiri. The present study assesses the source, degree, extent and nature of groundwater contamination in the Sirkazhi coastal region. Samples of groundwater were collected from 11 wells in this area and analyzed chemically to determine the extent of contamination. The results showed significant variations in water quality parameters in the study area and helped understand the longer-term adverse impacts that tsunami inundation can have upon groundwater resources.