Rendering the water using ue4

At first, while I add the terrain and imagery layer using cesium for ue4, how can I add water mask in cesium terrain using ue4 water plugin(https://docs.unrealengine.com/en-US/BuildingWorlds/Water/index.html) .

Second, If I have a tiff file which show where is water, how can i use water plugin to create a water mask in cesium terrain as the tiff file show.