Download the materials here. Place them in your project's content folder to use them.
These are free to use for any purpose, even commercially, without need for attribution. You are not permitted to sell a product where the majority of the product consists of this content or its derivatives.
I've included images below in case the files don't work for some reason. I created the materials in Unreal version 4.10 and have tested them in 4.12.
For the WorldPositionOffset input to look good the water mesh should be high poly. Making what would otherwise be a single quad high poly is a huge waste, so if you are looking for performance, just set this to 0.
You can also create very good looking and cheap waves using tesselation.
Just make sure the water mesh has a medium amount of polys to start with. See how the engine breaks them up by setting the view to wireframe while editing the material.