The effect of the preparation procedure—(variable amounts of hydrating water on the leachability of a soluble contaminant (CsNO³) from cement samples immersed in water, as well as the physical characteristics of cement samples such as density, pore volume, and compressive strength—were considered in this work. Leach tests of cement specimens containing 2% in weight of cesium nitrate (CsNO³), prepared at different water-to-cement ratios, W/C = 0.35, 0.40, 0.45, and 0.55, were cured for 60°C, 98% RH, for eleven days. The leaching standard procedure suggested by the International Organization for Standardization (ISO) was used to follow the kinetics for the Cs⁺, NO^3-, and Ca²⁺ releases from cement right cylinders, 20 mm in diameter and 20 mm high, leached in water at a solid surface-to-liquid volume (S/V) = 0.1/cm. The results of the cumulative fraction release (CFR) versus time (t) in days indicate that the leaching of soluble elements like NO^3- and cesium follows a diffusion mechanism. The cumulative fraction release (CFR) values were found to depend on a porosity factor β=(Vp)1,2,3...(Vp)0 where (Vp) 1,2,3 … represents the total porosity of cement at the W/C considered, and (Vp)⁰ represents the porosity at W/C = 0.35. A diffusion coefficient, De = 1.4 × 10^-7 cm²/s, calculated by the values of the cumulative fraction release at 50°C and W/C = 0.35, confirms our previous results obtained on cement samples containing CsNO³ and prepared under the same conditions.