四分律比丘含注戒本 2.734

2.734

水澆者，取大海水、白牛右角，收拾種子，置金輦上，諸小王輿，大婆羅門以水灌王頂。是剎利種，如是立王，故得名也。若婆羅門、毘舍、首陀如是立者，亦名「灌頂」也。

Regarding "sprinkled with water": Taking water from the great ocean in the right horn of a white ox, seeds are gathered and placed upon a golden carriage; with the lesser kings bearing the carriage, the great brahmins sprinkle the king's crown with the water. One of kṣatriya lineage anointed as king in this manner therefore obtains this title. If a brahmin, vaiśya, or śūdra is consecrated in this manner, it is also called "anointed on the crown."