1)enter free camera 2)open world editor 3) press f1 4)select the tool in the left sidebar that has the arrows. 5) find the water folder/item in the scene tree 6) click and drag on z axis
what the hell did you not understand? narwhal gave you a step-for step tutorial! you open the editor using "f11" by the way, it only works if you are in windowed mode (in case that was your problem...).