  In the general context of rotational water waves with a smooth vorticity it
is shown that the wave profile can be recovered from the horizontal component
of the velocity field on a line of symmetry. The method, which applies to waves
of finite and infinite depth, uses only the values of the horizontal velocity
of particles located on the line of symmetry that are close to the wave
surface. In fact, together with the wave surface we recover also the velocity
field in a suitable surface layer. The explicit recovery formula is valid under
the assumption that there are no stagnation points in the fluid for both
periodic and solitary waves in each of the three regimes of gravity,
capillary-gravity, and capillary waves. The efficiency of this method is
illustrated in the context of the explicit solutions provided by Crapper for
periodic capillary waves and Gerstner for periodic gravity waves.
