The table was constructed from ¼ inch thick plexiglass.  It is square: 1 meter on each side.  The lip of the table, essential for holding in the water, is 1 inch tall.  This allows an adequate depth of water to stand on the table, so that disturbances propagated through all of the water.  To cover the table fully, I used about 12 litres of water.

For many demonstrations, reflections of waves off the walls of the table is undesirable.  To prevent these reflections—which might confuse the audience of the demonstration—I lined the walls with kitchen sponges, slightly spaced to create turbulence, which reduces reflection.  This was not a perfect solution, but the sponges absorbed enough of the shock to prevent distracting reflection. 

To refine this system (and reduce setup time) I recommend constructing a fixed series of picket gates, to destroy the waves and eliminate reflection.  This can even be incorporated into the demonstration.

To make the waves used for demonstration, I used a function generator (set to generate low-frequency square waves) connected to a relay.  The function generator drove a signal, translated by the relay into up-and-down mechanical pulses.  With a variety of attachments, the relay creates steady disturbances in the water.

Single rod (generates simple circular waves)

Double rod (for demonstration of interference)

Flat bar, to generate wave fronts.  Useful for slit experiments.

For future demonstrations, I recommend use of a second relay, which would allow for more robust demonstrations of interference.  For example, a second relay, creating an opposite signal to the first one, can show negative interference and wave destruction.