This paper presents the long term behavior of EPDM geomembranes installed in 5 water reservoirs as well as in one experimental field in Spain. The initial properties of the EPDM geomembranes and their evolution over time have been measured regularly. This periodic testing was done on following properties: foldability at low temperature, hardness Shore-A, tensile properties, dynamic impact, puncture resistance. Samples were also evaluated using optical reflection microscopy and scanning electron microscopy. Additional tests were carried out to check the influence of orientation, thickness and exposure to UV. This document ends by giving some comments on the acceptable change of critical performance properties for an approximation of service life of EPDM geomembranes.