Possible error with water?

We may be doing this wrong, but our group is working on a remake to an old game for android.
However, when we use standard basic water, nothing at all happens.

We try to drag it into the terrain, but its got the “Not possible” symbol, or whatever thats called.

Help would be very appreciated.

You aren’t supposed to drag it into the Terrain.
If you wan’t to use the stock water just drag the water prefab to the scene.