The effects of confinement in nanotubes on the hydrogen bond structure of liquid water are studied by molecular dynamics simulation. Water has been described by means of a flexible version of the SPC potential of Berendsen et al. The carbon nanotube is modeled by a soft potential wall of the Lennard-Jones type. Our results indicate that the averaged number of hydrogen bonds decreases when we compare with bulk water and it is roughly independent of the tube radius excepting for very narrow tubes, which suffer a dramatic destruction of the H-bond network. The comparison with rigid cylinders indicates that this is a purl confinement effect.