Script that changes terrain properties not working. How do I fix this?

I am making a script that changes the water speed and wave size. It is not finished, but after testing it, nothing changes.

script.Parent.Terrain.WaterWaveSpeed = 10
script.Parent.Terrain.WaterWaveSize = 0.15
wait (10)
script.Parent.Terrain.WaterWaveSpeed = 65
script.Parent.Terrain.WaterWaveSize = 2
wait (30)

I have checked the output, and there is nothing there. I removed the Terrain part, and it doesn't fix it.