Abstract: The mathematical analysis of water waves is an intriguing and challenging subject. Even in the setting of a perfect fluid (incompressible and inviscid) the governing equations are highly intractable, primarily due to strong nonlinearities, compounded by the presence of an unknown free-boundary. This talk presents results concerning excess energy densities for exact nonlinear water waves. We prove that the excess kinetic energy density is always negative, whereas the excess potential energy density is always positive, for nonlinear water waves which are periodic, travelling and irrotational. A characterisation of the total excess energy density as a weighted mean of the kinetic energy along the wave surface profile is also constructed.