A differential equation is a mathematical equation that relates some function with its derivatives. Many fundamental laws of physics and chemistry can be formulated as differential equations. In biology and economics, differential equations are used to model the behavior of complex systems. The study of differential equations is a wide field in pure and applied mathematics, physics, and engineering. The shallow water equations are a set of hyperbolic partial differential equations (or parabolic if viscous shear is considered) that describe the flow below a pressure surface in a fluid (sometimes, but not necessarily, a free surface). Keywords: differential equation, shallow water equations, viscous shear, pressure surface etc.