The profile of water jets along its length before breakup is indirectly inferred from the observation of surface waves created by the jet as it plunges into a reservoir of pure and contaminated water. The inference isdrawn based on the measurement of surface wavelengths as a function of jet length before it touches the reservoir surface. It is observed that the nature of variation of wavelength changes abruptly at a certain jet length L$_0$. It isfound that the dimensionless L$_0$ depends only on the local velocity and diameter of the jet at L = L$_0$ apart from the local acceleration due to gravity but is not a function of the surface tension of the reservoir; i.e., L$_0$ is a functionof the Froude number Fr at L = L$_0$. Our analysis suggests the existence of an intermediate length scale L$_0$ that demarcates the inertia-dominated region (L ${\le}$ L$_0$) of the jet from the gravity-dominated region (L > L$_0$).