I use coffee not water. The surface is a lot like black ink without the inky mess. It also negates the need for a black bowl. If you do use water, I suggest placing a tumbled quartz crystal in the bottom (the round ones) and use that as a focal point. The quartz energy also aids in the scrying.
Seeing that I live in a city, I use natural spring water out of a bottle. I have collected rain water in the past but unfortunately due to the pollution in the air, it tends to look very dirty and smell. I know, it's sad, but it's the way it is. People are destroying the beauty of this world.