Abstract: Water tanks are containers for storing water. The need for water tank remains from olden civilization till date to supply stored water for many applications and processes such as drinking water, irrigation agricultural, fire suppression, agricultural farming, chemical manufacturing as well as many other uses. An Underground water storage tanks (or sub-surface tanks) is used for storing potable drinking water underground, wastewater & rainwater (from rain water harvesting) collected. It is a water storage structure constructed below the ground. This also includes structures which are partly below ground. This project gives in brief, the theory behind the design of liquid retaining structure i.e. rectangular underground water tank. This report includes design of a RCC underground rectangular water tank for required water demand.

| DOI: 10.17148/IARJSET.2022.9902