Key message Separating the internal (ontogenetic) and external (environmental) components of maritime pine development during controlled soil water deficit helps to highlight the plastic response. The adjusted measurements reveal significant differences between families for their plastic response for several physiology and growth traits. Context Soil water deficit is and will be a growing problem in some regions. Pinus pinaster Ait. is a species of commercial interest and is recognized as a drought-avoiding species. It is thus of interest to evaluate the adaptation potential of P. pinaster to soil water deficit. Aims This paper aims to estimate the plastic response to the variation of water availability at the family level (half-sibs). Methods Two-year-old P. pinaster cuttings from four families were submitted during 6 weeks to two contrasting watering regimes. The experiment started in April 2011 shortly after sprouting. The photosynthesis and stomatal conductance to water vapor were measured on 1-year-old needles. Intrinsic water-use efficiency was calculated as the ratio of photosynthesis to stomatal conductance. Radial growth, length of terminal shoot, and total height were also measured. The ontogenetic component of tree development was estimated on the well-watered trees for all the traits. Then, this development effect was eliminated from the data collected on the trees submitted to the soil water deficit in order to keep only the effect of this soil water deficit. Results After 6 weeks of reduced watering, the value of all adjusted traits decreased. An average plastic response to the variation of water availability was found to be significant and variable at the family level for the six adjusted variables. Conclusion These results suggest that there is genetic variation of phenotypic plasticity to drought in P. pinaster for several traits, including stomatal conductance, which appears to be a promising variable for future selection for resistance to drought.