Recommendations for the most likely values of the critical parameters of light and heavy water as accepted by the International Association for the Properties of Steam are presented, together with an assessment of their reliability. The results are, for H2O:Tc=(647.14+&dgr;1)K, &dgr;1=0.00±0.10;Pc=(22.064+0.27&dgr;1±0.005) MPa; &rgr;c=(322±3) kg/m3; and for D2O:Tc=(643.89+&dgr;2) K, &dgr;2=0.00±0.20;Pc=(21.671+0.27 &dgr;2±0.010) MPa; &rgr;c=(356±5) kg/m3. Supporting material for these choices of values and the assessment of their reliability is provided. Temperature values are on the International Practical Temperature Scale of 1968 (IPTS 1968) unless otherwise indicated.