Why Water Isn't a Great Conductor

If the surface of a material is rough, light goes in there and it bounces around between all of the imperfections in the surface. If you polish a material until smooth, that simply doesn't happen. The light hits the surface and bounces straight back out again in a concentrated, highly directional beam. And if you're standing at the correct angle, that light will bounce directly into your eye, and you will perceive it as a shine. As a result, pure water does not conduct electricity. It's an insulator.