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I suppose that this depends on what you want your water to do. Do you intend a water simulation (you mention that the model is static, so I imagine not)? Do you want any animation, and if so, do you want the geometry itself to animate, and if so, how? Do you want anything other than a flat surface (waterfalls, for example)?
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Once again this is likely to depend to some degree on your project, and in particular whether your selection is entirely 2D, or more 3-dimensional. If you can do with selecting from a plane, try the answer in this thread. If you want to pick 3D objects, then try this manual page. (In both cases you might want to look into Panda’s collision system, since both use it, I believe.
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Panda’s DirectGUI might serve your purposes, but I believe that there are a few other GUI systems available - try a forum search and you may find some. (I’m afraid that I don’t think that I’ve investigated any of them in any real depth myself.)