The construction of the water tanks depends in a great extent on its application. Essential factors in the construction of the tank are external factors which affect the tank, tank location, type of materials it stores etc. This paper presents the calculation of a tank filled with water. It describes how the tank behaves during wind and earthquake loads. The mutual influence of one component on the other will be analyzed. The support structure and the tank will be described. The introductory part will define the basic purpose of the fluid tank and carry out the basic distribution with respect to the purpose of the reservoir. The second chapter will refer to plate theory, more specifically, it will show a basic circular plate calculation that must meet the conditions in which it is located. The third chapter, also the most important for the calculation, refers to the theory of shell. The basic conditions and limitations for the shell will be described. Also, the equations that will be used in the main calculation will be explained. The fourth chapter covers the theory of rods which is important for the calculation of the support structure. Bending and bending of the rods will be considered. The fifth chapter refers to the European standard EUROCODE, which will briefly describe the basic equations used in the tank calculation. In this paper, no wind and earthquake effect will be taken into account when calculating the final calculation. The sixth chapter will show basic diagrams that will be derived from the calculation and will provide the explanations and descriptions of the mentioned diagrams. The seventh chapter refers to the proposal of the tank support in order to be environmentally safe. In the eighth, final chapter, all the chapters will be summarized and drawn to provide a unified conclusion.