From Hindupedia, the Hindu Encyclopedia
By Swami Harshananda
Aponaptriyā is a minor ritual conducted during the Somayāga. Water is drawn from a river on the day prior to the extraction of the soma juice and preserved in a vessel called vasatīvarī. Then the water drawn on the morning of ritual extraction is kept in vessels named ekadhanā and ceremonially mixed with appropriate hymns.
This hymn is also known by the same name as the rite itself. The hotṛ (priest, representing the Rgveda) is advised to recite the first stanza (pra devatrā brahmaṇe ...) continuously thrice. This will induce Parjanya, the rain-god, to give rains where and when necessary.
This rite will also help the yajamāna (performer of sacrifice) to complete the sacrifice without any obstacles or hitch.
- The Concise Encyclopedia of Hinduism, Swami Harshananda, Ram Krishna Math, Bangalore