The Water balance of Veeranam Lake is calculated by considering all inflow and outflow components of lake. Inflow components of Veeranam lake include direct rainfall, Vadavar River inflow, ungauged catchment inflow whereas outflow components of the lake include evaporation and discharge of water for various activities (CMWSSB pumping outflow, Irrigational outflow, Lalpet Weir outflow, VNSS outflow). Ungauged catchment runoff to Veeranam Lake is estimated by Soil Conservation Service-Curve Number (SCS-CN) method. About 42% of rainfall volume in the catchment is infiltrated into the ground and 58% of rainfall volume, flow as a direct surface runoff into the Veeranam Lake. Groundwater inflow and outflow to lake are commonly expressed as net groundwater exchange and it is estimated as 53% of total outflow components of the lake. Veeranam Lake is dominated by both the inflow and outflow components of the lake. The calculated net groundwater exchange is negative and this indicates that Veeranam Lake recharges the nearby aquifer zones. © EM International.