Waterball
A waterball is a nice and firm ball of water compact and floating through the air. It differentiates itself from the bubble by not being hollow on the inside. It contrasts the fireball by being refreshing, quenching, and blissful.
Encounters
A waterball can be encountered by trilling a flute on the shores of a tropic ocean. It will rise from the waves and float around a bit. It will then fly forward in a random direction. Waterballs burst upon contact with any solid surface and thus are fleeting.
Implications
The existence of a waterball is what led scientists to discover the necessary diametric fireball. The surface of a waterball displays reflections for up to 40 hours after they were first imprinted, so particularly deeply sourced waterballs offer low-resolution glimpses into undersea life.
It is presumed that, if frozen, it will turn into an iceball. Similarly, when boiled, it will vaporize into a steamball.
Exile
Waterballs were exiled from the Holy Roman Empire in 1206. This was widely considered a paperwork error but was never fixed due to policy.