The growing deployment of ground-based photovoltaic plants in the last decade has increased competition for land and associated acquisition costs. Installation of floating photovoltaic (FPV) in existing hydropower reservoirs offers a solution to limit land use while providing solar electricity, leveraging water bodies, and reducing evaporation losses. This study assesses the potential electricity output of FPVs at regional and national levels in the EU considering three reservoir area coverage scenarios (full-100%, 10%, 1%) and one in which the FPVs have an installed capacity equal to the corresponding hydropower plant. Estimation of the evaporation and water losses for individual reservoirs as well as the water savings considering two types of floats are also analyzed using climatic parameters for the year 2018. Findings reveal that covering 2.3% of the total area of EU reservoirs with FPVs has the potential to generate 42.31 TWh annually when doubling the installed capacity of the hydropower reservoirs. The total water losses are estimated to be up to 9380 mcm and the installation of FPVs can potentially save from 450 to 9380 mcm of water per year. At the national level, France, Portugal, and Spain are the countries with the highest potential water savings. Most of the countries analyzed can produce over 50% of the existing hydropower generation capacity in the same reservoirs by installing FPVs in less than 15% of the total available reservoir area. The FPVs' multi benefits and the existing hydropower potential are compatible with the EU’s ongoing energy transformation and outgrowth.