Abstract—Seepage through water tank walls is one of the most important phenomena can get the operation into trouble. This paper introduces water seepage through cracked and non-cracked segments by corresponding theories for operation limit states and models governing parameters' uncertainties with random numbers. The probability of failure and reliability index of tank segment cracked concrete has calculated by Monte Carlo simulation. It is essential to have crack width extension model to estimate operation lifetime in tanks due to the crack width that often expands over time. Also, the probability of leakage starting during operation lifetime is calculated for non-cracked segments and sections which should be watertightness. In this type of structures, reliability analysis method presented in this paper can be used in designing of minimum width required and determination of concrete mix design properties and permeability by definition acceptable risk in structure lifetime.