Slowly spin the fountain and look at the trajectories of the water jets. The water in the pipes rotate around the centre. The further from the centre the water gets, the faster it rotates. The water coming out of the inward-facing pipes has a greater rotation speed than the water coming out of the shorter pipes. This means that the water jet going inwards will go with the direction of rotation.
The same thing happens in a 400-metre dash. When the runners are next to each other in the curve, and the runner on the outside track manages to keep up with the one on the inside track, maintain their speed and then switch to the inside track, they will be able to outrun the others in the race.
The French scientist Coriolis studied this phenomenon in the 1800s, when he noticed that air currents heading northwards always turn off to the east in the rotational direction of Earth.
To learn more, you can check out the experiment “Earth in a Bottle” in the water section.