We investigated the effect of water constraints on yearling Lacerta vivipara, a widespread species of lizard inhabiting European peat bogs and heath land. We conducted a laboratory experiment to investigate plasticity of growth rate, activity level and preferred body temperature. We subjected individuals of two source habitats (dry vs humid) to two laboratory conditions of water supply resulting in different air relative humidity and water availability (high vs low). We observed that a low water supply induced a lower growth rate and lower activity level, suggesting that growth limitation is correlated with adaptive responses to avoid dehydration. However, individuals from the two habitats selected different body temperatures when restricted in water and showed different ratios between growth and activity. This suggests that there is population variability in phenotypic plasticity with respect to water availability in the habitat. Field observations conducted in six natural populations, classified into two groups (dry vs humid habitat) also suggest that growth rate in nature is constrained by water availability.