Needle-sized spouts and returns packed together in a solid media. Water is pumped from the common return tank to the always-full feed tank under high pressure which feeds the spouts. Additionally a pump continuously evacuates the air out of the larger return-tank to keep water from pooling on the floor of the fountain.

Spout/return sizes and system pressure specs are determined by the requirements that a person standing or walking will not lose their footing, but a person who is laying down and thus has their weight distributed over a much greater surface area will be able to slide across the rink on the tips of the water streams (like a disk on an air-hockey table).

And during the winter it's a hockey rink of course :D