Nordpark fountains in Dusseldorf again

I've been thinking about why the beam of water from the fountain spreads out as it goes through the air and doesn't stay as a narrow beam. I suspect that it is because the water flows through a pipe so that the water nearest the outside of the pipe will experience friction and move slightly slower than that at the middle of the flow. The slower water won't go as far. If the water is projected at angle theta to the horizontal, then horizontally the water will have speed v.cos(theta) and vertically v.sin(theta). Vertically, it will reach its highest point after time t=vsin(theta)/g and symmetrically will mean it hits the bottom after time t=vsin(theta)/g. Assuming horizontal speed is constant then distance horizontally will be v.cos(theta).t = vsquared.sin(theta)cos(theta)/g. The ratio of biggest speed/smallest speed will then be square root (smallest distance/biggest distance). For the fountain in the bottom left hand corner this will be about 1.07. The speeds are not too different.