Water is essential for agriculture. Most of the farmers depending upon the ground water for irrigation purpose, but now a days the underground water is going to towards very deep down level. Because our environment affected by water drought, pollution and lack of rain falls. It will be creating negative effects to cultivation .In this present study is to assess the underground  water quality in Mayiladuthurai Taluk of Nagapattinam District in Tamil Nadu. Totally 30 underground water samples were collected, which covers 10 Revenue villages in Mayiladuthurai Taluk, 3 samples from each Revenue village and analyzed all the physico - chemical parameters such as pH, EC, Ca, Na, K, SO4, Cl, Mg , CO3, and HCO3 and the water quality index SAR, RSC, Geo-chemical types, classification were determined by standard methods, standard calculation  and by using standard instruments. Then the irrigation water quality results were compared with standard values Recommended by World Health Organization (WHO), Bureau of Indian Standards (BIS) and Indian Council of Medical Research (ICMR). The proposed work is very essential not only for crop production but also to maintain soil fertility, to maintain hazardous free environment and to enhance the living standard and in turn to uplift our Agriculturist.