In recent years, the floating photovoltaic (FPV) market has undergone significant expansion, fueled by the multitude of advantages inherent in this installation method. Notably, it is an alternative to face the lack of available ground surface and it could lead to a substantial reduction in reservoir evaporation. Indeed, the components of FPV arrays partially cover the free surface, mitigating the effects of wind at the surface of the water which in turn should limit the evaporation. Given the increasing importance of water as a critical and scarce resource, the need to find ways to conserve water has never been more pronounced. Presently, the estimation of evaporation relies mainly on empirical laws, and variables such as local wind, ambient humidity, air and water temperature, as well as FPV array characteristics have a significant influence on evaporation dynamics. To address these challenges, our study introduces a novel approach utilizing Computational Fluid Dynamics (CFD) simulations to model micro-scale conditions above a reservoir partially covered by an FPV power-plant and surrounded by the ground. In this study, the plant is modeled by an equivalent rough surface and the water vapor transfer is taken into account through a mass exchange coefficient. These quantities are imposed using correlations derived from 2D bi-periodic models, primarily based on wind characteristics (friction velocity, wind directions). However, as the water flow in the reservoir is not modeled, the water surface temperature is a critical parameter because it is a boundary condition which is often an unknown variable. Therefore, this study aims at investigating the impact of water temperature on reservoir evaporation rates, considering scenarios with two distinct FPV layouts that are compared to the evaporation on a reservoir without FPV array. The first FPV layout entails a large footprint system, characterized by a ground-coverage ratio (GCR) of 75 %, while the second FPV layout represents a free footprint system with a GCR of 57 %. The water-coverage ratio (WCR, namely the surface in direct contact with the waterbody, including floats, structure, buoy, or even directly the panel in certain cases), set respectively at 60% and 10%, is also a key indicator. This study will therefore enable us to conclude on the efficiency of these two types of layouts in terms of evaporation reduction, with a view to geometric optimization. Also, the influence of bottom conditions providing insights that guide us in determining a better approach for incorporating water temperature into our model.