  We propose a unified model combining the first-order liquid-liquid and the
second-order ferroelectric phase transitions models and explaining various
features of the $\lambda$-point of liquid water within a single theoretical
framework. It becomes clear within the proposed model that not only does the
long-range dipole-dipole interaction of water molecules yield a large value of
dielectric constant $\epsilon$ at room temperatures, our analysis shows that
the large dipole moment of the water molecules also leads to a ferroelectric
phase transition at a temperature close to the lambda-point. Our more refined
model suggests that the phase transition occurs only in the low density
component of the liquid and is the origin of the singularity of the dielectric
constant recently observed in experiments with supercooled liquid water at
temperature T~233K. This combined model agrees well with nearly every available
set of experiments and explains most of the well-known and even recently
obtained results of MD simulations.
