Castronomancy is a form of hydromancy, in which clues to the past, present, and future can be gleaned by studying images reflecting on a watery surface in a glass or magical vessel.

Pegomancy is related, and uses water from springs or sacred pools.

Some diviners will color the water use in black ink. This provides a surface which is more reflective. Those who use darkened water often select a particular receptacle to use as well, in hopes of an accurate reading.

The calm surface of water after being disrupted. There are many methods attributed to Hydromancy, including noting the ripples, color, ebb and flow of the water. Courtesy of Wikipedia.