The far-infrared spectrum of 18O enriched water vapour (40–700 cm−1)

•The far-infrared rotational spectrum of water vapour enriched in 18O is studied by FTS with a synchrotron radiation source.•Lines of about 2570 transitions of seven water isotopologues are observed and assigned for the first time.•142 new empirical energy levels are determined for H218O, H217O, HD18O, and HD17O.•Significant deviations are noted compared to HITRAN2016 line positions and to the energy levels recommended by an IUPAC-task group.