Reply to comment on 'supercooled and glassy water'

In a recent review on supercooled and glassy water (Debenedetti 2003 J. Phys.: Condens. Matter 15 R1669) I used a thermodynamic consistency argument to rule out the possibility, proposed originally by Speedy (1982 J. Phys. Chem. 86 982), that the spinodal curve for superheated liquid water can retrace to positive pressure. The argument is based on the impossibility that a thermodynamic state other than a critical point be a limit of stability (i.e., a point along a spinodal line) and simultaneously coexist with another phase. Speedy's comment offers a counter-example involving the freezing transition to argue that a thermodynamic state can in fact be a limit of stability (spinodal) and simultaneously coexist with a different phase (i.e., a non-critical point along the phase coexistence locus). Here I argue that instability to infinitesimal density fluctuations and coexistence with a different phase are mutually exclusive conditions.