Bing Wu Ding Wei Tianhe Shui (丙午丁未天河水) refers to the water of the Milky Way. Bing (丙) and Ding (丁) belong to fire, and Wu (午) is the place where fire is prosperous. However, the Nayin (纳音) is water, which emerges from fire. Without the Milky Way, it cannot exist, hence it is called Tianhe Shui (天河水).