Given the increasing decline of water resources in recent years, controlling and reducing water evaporation from open surfaces such as reservoirs and dams has gained significant importance. One of the modern approaches to mitigate evaporation losses is the use of covering fluids that form a thin monolayer over the water surface. In this study, the effect of the anti-evaporation fluid octadecanol on the evaporation rate of water was investigated. The experimental part of the research was conducted over a 20-day period using a Class A evaporation pan, during which key influencing parameters such as temperature, wind speed, and relative humidity were measured regularly three times per day. In the numerical section, the phenomenon was simulated using the Finite Volume Method (FVM) with a multiphase flow approach. The model consisted of four phases water, air, water vapor, and the covering fluid and the Volume of Fluid (VOF) method was applied to capture the interface behavior. The initial water height in the tank was set to 2.5 cm, and the transient analysis was carried out for a 30-minute period. After validating the numerical model with experimental data, the results indicated that the use of the covering fluid could reduce water evaporation by approximately 62%. The difference between the experimental and numerical results was around 10%, demonstrating the acceptable accuracy of the developed model.