Why does water never flow straight down the drain?

Question

it is always in a spiral.............

Answer 1

There is always a small amount of angular momentum (rotation) in the water. Normally you don't notice it, but when the water gets drawn inwards towards the drain the rotation gets faster, due to a principle called the conservation of angular momentum. Other examples of that are a skater spinning faster as she brings her arms in, and a slowly rotating weather system creating a tornado.

The commonly held belief about it being caused by the earth's rotation is a myth.

Answer 2

As the water approaches the drain, it gains momentum. If the momentum is not exactly toward the drain (which it rarely is), then the water will spiral in. That's the basic concept and it applies to other things like solar systems, galaxies, tornadoes and hurricanes.

Answer 3

I think because it's the shape of the drain itself.

if the drain opening were square, there would be no spiral.