Why do the streamlined flow of water tapers as it flow out from the tap?

Answer 1

I'm no scientist but I have a theory. I do know that water has a high surface tension(ST). This basically means that it sticks to itself. Alcohol would be something with a lower ST. Anyway as the water falls gravity tries to pull it down at a constant acceleration. There's a little thing called friction though that can slow it down. The water in the middle of the stream must flow against itself and because of its high ST it drags, but on the outside of the column it rubs against the air which it barely touches so it can accelerate faster. So with the inside water lagging behind and the outside water speeding up can you imagine the result? The outside water pulls in and you have a narrower column. It's all cause and effect.