Water falling, why does it spin?

I have noticed that water, when falling will rotate. Looking closely at a thin stream from a faucet and placing a flat object mid stream you will see the water is rotating. The further down the stream you go you will notice the rotation is much quicker. Am I confused at this occurrence or is there a reason? I can only come up with the rotation of the earth taking into affect.

• I doubt that it has anything to do with the rotation of the Earth. – user42733 Mar 31 '14 at 15:39
• Water does not spin coming out of my faucet. Assuming your faucet causes water to come out rotating, conservation of angular momentum would cause the water to rotate faster farther down the stream because the stream narrows farther down. – Brandon Enright Mar 31 '14 at 15:42
• Yes, the speed of rotation will increase because the stream becomes narrower. No doubt about that. What causes the water to rotate is difficult to guess. Could be the shape of the opening of the faucet. – user42733 Mar 31 '14 at 15:45
• It is very difficult to make a faucet, or pour from a cup, without imparting some rotation to the water. As @Parth said, it will rotate faster as the diameter of the stream decreases. – Mike Dunlavey Mar 31 '14 at 15:51
• I think the spin is caused by upstream bends in the water piping (slanted bends plus gravity). – Mirc Breitschuh Mar 31 '14 at 19:15