Handling cascading reservoir systems is an important energy management optimization problem. The difficulty of these problems stems, in part, from the modeling of the hydro-production function. Data are not always easy to come by. To remedy this issue, this paper proposes and describes a realistic instance generator, building instances of varying difficulty. No specific data format for these problems is currently available in the literature. In addition, both notation and formulations tend to vary widely. Instances and case studies are poorly available or otherwise not applicable to different variants of these problems. The purpose of the generator is also a first attempt to develop a shared data format useful for different variants of hydro unit commitment problems and seeks to mediate the needs of different sectors interested in the optimization of hydro power plants.