The study aims to evaluate the structural integrity of a rectangular tank that suffers from the effects of corrosion on receiving brackish water from the groundwater of the Lagoa Rodrigo de Freitas. The tank was originally designed to store water reuse and then later, implemented in the lowering system project of Lagoa Rodrigo de Freita s groundwater. It consists basically of ASTM A36 steel welded plates with three equidistant submerged pumps installed, which is responsible for pumping fluid to the culvert. The lowering system consists of 15 submerged pumps connected to the stations, which pump the water from the groundwater to the tank and then, into two main networks leading to the culverts. The evaluation study started with a failure analysis caused by tension on flat plates under nominal loads, taking into consideration the welds and corrosion. The results of stress, strain and fatigue of the tank, as well as the possible solutions to minimize corrosion effects will be presented in the present study.