The water reserve in France is the aggregated weekly average filling rate of all water reservoir and hydro storage plants, recorded on Mondays at midnight. It is expressed in MWh and is sent by the producers to RTE, which aggregates the data before publication. This data is published every Wednesday at 12.30 or the next day if Wednesday is not a working day.
The upper energy is the one that we can generate on the (only) production unit directly attached to the reservoir, depending on its filling rate. The data published constitutes the stock of those upper energies units.
The French maximum stock related to this calculus is 3591 GWh.