Water has been widely studied for its fundamental importance in science, engineering, and our daily life. Its molecular composition is simple: one oxygen atom and two hydrogen atoms. However, due to its intermolecular hydrogen bonds, water has many unique and sometimes anomalous properties, such as the density maximum at 4 • C and unusually high melting point. For a better understanding of these properties at the microscopic scale, molecular dynamics (MD) has been a useful tool. Various water models have been developed to describe the potential energy surface (PES) that governs the interactions within and between water molecules, enabling the predictions of many structural, thermodynamic, and dynamical properties of water from MD simulations. Among these water models, the simplest type is the so-called rigid non-polarizable model wherein the water molecule is treated as a rigid body with some fixed point charges assigned to atoms or sites, independent of its molecular environment. Despite its simplicity, a well-parameterized rigid non-polarizable water model, such as TIP4P/2005, 1 is able to accurately predict a wide range of properties of liquid water, such as density, isothermal compressibility, self-diffusion coefficient, etc. Furthermore, the high computational efficiency of these models makes them very popular in large-scale MD simulations involving water, such as biomolecular simulations. The greatly simplified description of water by the rigid non-polarizable model results in some flaws, and one of them is its failure in reproducing experimental dielectric properties, such as the dielectric constant, which depends on not only the PES, but also the dipole moment surface (DMS), namely the dipole moment as a function of configuration. This failure can be in large part attributed to the use of fixed point charges. In reality, the electron density of water will be redistributed in response to the change in its local molecular environment. Partitioning the electron density generates effective charges of atoms, often called partial atomic charges, which should change in response to changes in configuration.