Hyperelastic geomembranes have been used as rehabilitation technology in hydropower plants and hydraulic structures since several decades. Recently, their application has been extended to pressure waterways, where challenging flow conditions with high flow velocity and pressure occur. As geomembranes are thin and flexible structures with no bending rigidity, they undergo fluid-structure interactions with large and hopefully reversible deformations when subjected to external loads. This paper focuses on fluid-structure interactions of hyperelastic geomembranes and presents the results of experimental tests conducted to assess the steady flow-induced deformations of hyperelastic geomembranes and subsequent stationary head losses for an optimized application in pressure waterways. Results confirm that geomembranes undergo large out-of-plane deflections when subjected to fluid-structure interactions, depending on flow conditions. In addition, the impact on subsequent stationary head losses is characterized.