The second-critical-point scenario is one of the most popular explanations for the anomalous behavior of supercooled liquid water. According to this scenario, liquid water at ambient conditions is a "supercritical" fluid that separates into two types of liquid water in the supercooled region. However, experimental confirmation is challenging. In this work we developed a scaled parametric equation of state, based on the principle of critical-point universality, to examine the second-critical-point scenario from a new direction. The equation of state, built on the growing evidence for liquid-liquid water separation, is universal in terms of theoretical scaling fields and belongs to the Ising-model universality class. 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" (locus of stability minima) and determine that the critical pressure is considerably lower than predicted by computer simulations.