Impose reflections but not render the model

[g.synetos]

Hello all,
What i would like to achieve is to have a surface that will not be rendered but it will impose reflections on the rest of the objects.
To be more specific i have a flat area which has water properties,
I want to render using a background image but keeping the only the reflections that are being imposed to the other objects from this water surface.
Any idea how i can achieve that?

Thank you very much in advance

[Micha]

If you enable the advance mode for your material than you get the raytrace options visible and there you can disable "visible to camera".

But you will get the water reflected light only if you start to work with enabled caustic.But I haven't so much experience with caustic.

[g.synetos]

Excellent Micha I found it! Thank you very much!