  We have developed a scaled parametric equation of state to describe and
predict thermodynamic properties of supercooled water. The equation of state,
built on the growing evidence that the critical point of supercooled
liquid-liquid water separation exists, is universal in terms of theoretical
scaling fields and is shown to belong to the Ising-model class of universality.
The theoretical scaling fields are postulated to be analytical combinations of
the physical fields, pressure and temperature. The equation of state enables us
to accurately locate the "Widom line" (the locus of stability minima) and
determine that the critical pressure is considerably lower than predicted by
computer simulations.
