A singular thermodynamically consistent temperature at the origin of the anomalous behavior of liquid water

The density maximum of water dominates the thermodynamics of the system under ambient conditions, is strongly P-dependent, and disappears at a crossover pressure P(cross) ~ 1.8 kbar. We study this variable across a wide area of the T-P phase diagram. We consider old and new data of both the isothermal compressibility K(T)(T, P) and the coefficient of thermal expansion α(P)(T, P). We observe that K(T)(T) shows a minimum at T* ~ 315±5 K for all the studied pressures. We find the behavior of α(P) to also be surprising: all the α(P)(T) curves measured at different P cross at T*. The experimental data show a "singular and universal expansivity point" at T* ~ 315 K and α(P)(T*) ≃ 0.44 10(-3) K(-1). Unlike other water singularities, we find this temperature to be thermodynamically consistent in the relationship connecting the two response functions.