D/H ratio in cometary water as a function of the active fraction computed from the water production rates measured at perihelion. The uncertainties on the active fraction (horizontal error bars) include a 30% uncertainty on the water production rates (Combi et al. 2019) and the uncertainty on the nucleus size. The color of each symbol indicates a comet; see legend at right, where the dynamical class is also indicated: Oort cloud (OC) or short-period Jupiter-family (JF) comets. The blue horizontal line corresponds to the VSMOW D/H value. The upper limit for the D/H ratio in comet 45P is indicated by a downward arrow and the lower limit for the active fraction in comet 2009P1 by a right arrow. The dash-dotted line shows the expected D/H assuming two sources of water: D-rich (3.5 × VSMOW) from the nucleus and D-poor (VSMOW). Comets with an active fraction equal to 0.08 are assumed to release only D-rich water.