Water and fire were the elements honored by the Zoroastrians, Stone Age pastoralists. They were similar to the proto Indo-Iranians who personified water as goddesses, the Apas, praying to them and offering librations called zaothra, in Avestan, meaning offering in general. In Zoroastrianism, the libration of water consisted of three ingredients: milk, the sap, or leaves of two plants. These ingredients represented the plant and animal kingdoms which are nourished by water; and thus, consecrated by prayer, the zaothra was believed to return to that element the vital force which it had given out so to return its purity and abundance. It is speculated in ancient ties such librations were performed in each household by the nearest pool or spring, as well as being a priestly function.
The other chief cult object was fire. It was essential to almost every aspect of the lives of these steppe-dwellers; it warmed their houses in bitter winters, was used for cooking meat of wild or domestic animals which provided their stable diet, and so on. To Indo-Europeans, it was important to keep the fire in the hearth continually burning. Agni, fire-god, was honored by the Brahmans, the Zoroastrians called him Atar. The made a three-fold offering to fire consisting of clean-dry furl, incense, probably dried leaves of herbs, and a small portion of animal fat. This was the zaothra to fire which was similar to the one to water. Fire, like water, was strengthened by the offerings from the plant and animal worlds; fuel and incense were probably given thrice daily at times ordained for prayer, sunrise, noon, and sunset, while the fat was presumedly offered whenever the family had meat to cook. The fire surely received it share of the fat which was visibly seen when it blazed up.
The belief for these water and fire offerings formed the daily priestly act of worship, called by the Iranians the yasna” by the Indians the yajna (from the verbal root yaz- “sacrifice, worship”). At this service the zaothra to the fire was obtained from a blood sacrifice that evidently was made regularly. The Indo-Iranians felt a sense of awe and danger at taking life, and never did it without consecrating the act by prayer, whereby, they believed, the creature’s spirit would be able to live on. The strong kinship felt between man and beast was expressed in the ancient part of the yasna liturgy. A.G.H.
Boyce, Mary, Zoroastrians: Their Religious Beliefs and Practices, New York, Routledge, 2002, pp. 3-5