In this paper, based on regular solution theory, a general equation for the calculation of different kinds of liquid-liquid equilibria (LLE) containing water is developed. A mixing entropy term and a long-range electrostatic term are introduced. A relationship between the interaction parameter and the absolute temperature is proposed. It can be used to correlate the LLE data for water-organic binary systems with upper and lower critical solution temperatures. The general equation has a wide application to LLE containing water-organic and water-electrolyte binary systems, as well as water-organic-organic and water-organic-electrolyte ternary systems. A simple equation for predicting the critical composition for binary LLE is deduced.