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.