"Heaven, Earth and Water"

or more precisely
"Upper World, Middle World, Lower World",
because this is the Vertical of the Universe, not the elements. Therefore, the Earth, for example, is red, not black in the color of the soil, with a center and four cardinal points.
Black (or rather dark) here, the Water is both a maze and a Snake (then the upper fork can be understood as an open mouth, and the spiral as the body of a Snake).
Well, in general, it is drawn with thoughts of rain. Rain as a link between the Upper and Lower worlds (in folk magic, through underground water (wells), they tried to influence the heavenly water and cause rain).
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