The water tank is a structure used to store water for supplying to households for drinking purposes, for industries as a coolant, and irrigational water for agricultural farming in some areas. Water tanks are classified on basis of their shapes and position of structure. In this paper, we had discussed the design of an underground water tank of Rectangular shape that is Designed and analyzed using Staad pro. Underground water tank faces a different type of loads compared to other structures, they mainly face horizontal or lateral loads due to earth pressure and water pressure or any liquid pressure which is been stored in the tank. The sidewalls of the underground water tank will face greater load at the bottom and the load linearly decreases towards the top.