Water

Apas is the water tattva, one of the five gross elements or mahabhuta of the Indian elemental scheme, the principle of fluidity, cohesion, taste and flow. In the classical analysis each of the five elements is linked to a sense and a subtle essence: water is associated with the sense of taste and, in the subtle physiology of the body, with fluidity, the sacral region and the waters of the organism. The tattvas belong to the Samkhya and Tantric metaphysics of India, where they are stages in the unfolding of manifest nature from its subtle roots.

The element passed into Western occultism through Rama Prasad's Nature's Finer Forces of 1890 and the Golden Dawn, which used the tattva symbols, water represented by a silver crescent, as objects of meditation and "tattva vision" from 1888. That adoption is a modern Western development; the water tattva itself and its attributes of cohesion and taste are part of the far older Indian doctrine of the elements.

Sources Classical Samkhya: An Interpretation of Its History and MeaningGerald James Larson with Nature's Finer Forces: The Science of Breath and the Philosophy of the TattvasRama Prasad

The Hermetic Order of the Golden Dawn, in its late nineteenth century synthesis, adapted Apas into a silver crescent, one of five coloured shapes used as meditation and scrying cards, a practice built alongside rather than descended from the tattva's original role in Indian philosophy. The crescent's curve and pale colour were chosen to evoke water's fluidity and its traditional association with the moon, reflected light rather than fire's own heat.

In Golden Dawn method the practitioner gazes at the painted crescent until an afterimage forms, then holds that image with closed eyes as a focus for meditation or visionary work, treating each of the five tattva cards as a distinct gateway; the technique was carried forward largely unchanged by later occult currents that inherited Golden Dawn material, including some Thelemic practitioners.

This card based practice is a later Western invention layered onto a borrowed vocabulary, and it should be read as such rather than as evidence of how Apas functions within its own Indian sources, where it names a physical and physiological principle, the fluid and cohesive, tied to taste and the body's fluids, rather than a shape used for visionary gazing. The two uses can be described side by side without treating one as an explanation of the other.