Zi is the first of the Twelve Earthly Branches, belonging to Yang Water, associated with the Rat zodiac sign, and corresponding to the Zi Hour (11:00 PM–1:00 AM). Zi Water represents winter water—cold, deep, and profound—symbolizing wisdom, agility, and latent power. In a Bazi chart, Zi Water embodies the 'Ink Pond', indicating literary talent and scholarly aptitude.
Zi Water is identified from the Earthly Branches in the Four Pillars of Destiny. If Zi appears in the Year Branch, the native belongs to the Rat zodiac; if Zi appears in the Day Branch, the Spouse Palace is Zi Water. Zi Water is strongest during the Zi Month (lunar November).
A person born on a Jia-Zi Day has Zi Water as the Direct Seal in the Day Branch, indicating a spouse who is both intelligent and culturally refined.