Accelerated ageing was performed in distilled water at different temperatures (25, 30, 40 and 50°C) on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), which is a biodegradable biopolymer, in order to estimate its lifetime in aqueous environment. In a first part, degradation mechanisms were followed by gravimetry, tensile tests and steric exclusion chromatography. Both immersion and relative humidity have been examined. In a second part, the strain at break was used as an indicator for lifetime prediction with an Arrhenius extrapolation. The study revealed the presence of only one irreversible degradation mechanism, i.e. hydrolytic degradation, which is temperature dependant. So, within the approach assumptions, the lifetime in distilled water of PHBV following Arrhenius behaviour can be predicted.