Maybe not an answer at all but...

The shape makes me think of cavitation. But everything I find suggests that cavitation can only happen at high pressures.

What I see is the water being spread into a cone by the inner restrictor. Because the pressure is low the water does not seperate into droplets so surface tension pulls the water back towards the center of the flow. As the pressure is increased the water forms droplets, surface tension is broken and the water continues to flow outward in a cone shape.

While water can carry a static charge, I do not think electrical charge would pull the water back togeather for two reasons: first, the charge of the water would be the same causing a repulsive effect, and second the charge would be very weak and not able to pull the water back towards the center of the flow.

The closest description of the shape I could find would be a prolate spheroid, or football shape.

Well it's 20 hours into a 24 hour work day and science make grunt head hurt. So let's get some science/math types to help out here.