Groundwater selling is a guarantee against deficiency rains in areas where farmers do not have access to surface water irrigation. Therefore, examination of groundwater market development and the efficiency of groundwater use under different water regimes needs to be studied. The objective of the study was (a) to analyse the structure and contact of groundwater markets and (b) to estimate the cost of ground water extraction and selling price in Hosur and Kaveripatinam taluks of Krishnagiri district, Tamil Nadu. Based on the Primary survey, water structures were analysed using simple statistics and measured efficiency by Data Envelopment Analysis. The groundwater market structure demonstrated that the number of irrigation water buyers grows as the size of the farm decreases, while the number of irrigation water sellers grows as the size of the farm increases. The efficiency of groundwater use is estimated by data envelop analysis. According to the data, in a sample of groundwater markets, the seller-buyer concentration ratio was 1:1.13. The cropping intensity and irrigation intensity were highest (89.13 and 93.19 %, respectively) for the self-user+seller category. The selling price of groundwater (Rs. 50 per tank) was marginally higher than the total cost of water extraction (Rs. 28.27 per tank), thereby implying the exploitative nature of groundwater markets. According to findings on input consumption and landholdings, water buyers are resource-strapped farmers who are unlikely to be able to afford the large investments required to install a well.