SoCraftastic tested six marker types on a non-porous surface to see which one allowed the ink to float on water. The effect is pretty cool with a stick figure.
It turns out the only brand that really works well is Expo dry erase markers:
The other trick is to find the right non-porous surface. The clear Pyrex worked OK, but a white glazed ceramic plate did the job much better.
• DRAWING ON WATER (YouTube / SoCraftastic)