MR diagram of water-rich planets (f_H2O ≥ 0.45) around M_⋆ =  0.4 M_⊙ (circles) and M_⋆ =  0.7 M_⊙ (diamonds). Black-bordered symbols indicate f_HHe ≤ 10⁻², while grey, f_HHe > 10⁻². The colour bar is the equilibrium temperature of the planets at zero albedo. The dashed-blue line shows the condensed-water line, the light-blue dashed a fitting MR relation to the steam worlds, described in Sect.B.5.