I was tempted to make a reference to "Snakes on a Plane" - but I won't.
For the best results you should use a shader. It gives a higher quality and more realistic effect than other methods. Having said that, there are a couple of ways I can think of to do a quick water effect:
1) You could create an animated GIF of moving water and texture your plane with that. It would probably need to be seamless (so the edges weren't detectable). Animated GIF's are supported by AppGameKit Studio and can even be used as a 3D object texture BUT they can slow the app down quite considerably due to the work involved in rendering them. By their nature they also have limited colour palettes so can look pixelated - but that may be a style you are after.
2) You could use a static texture - like a seamless JPEG or PNG of water, and then use the SetSpriteUVOffset command to slide the texture over your plane or any other 3D object. This will give the impression that the water is moving like a stream. This is the simplest method and if you make your object slightly translucent it can look quite good, but your water will still be flat, i.e. no 3D waves.
I would recommend looking into the shader method though if you want realism and your target devices support it.
