Article snapshot taken from Wikipedia with creative commons attribution-sharealike license.
Give it a read and then ask your questions in the chat.
We can research this topic together.
Ap (áp-) is the Vedic Sanskrit term for "water", which in Classical Sanskrit only occurs in the plural āpas (sometimes re-analysed as a thematic singular, āpa-), whence Hindiāp. The term is from PIEhxap "water".
The Indo-Iranian word also survives as the Persian word for water, āb, e.g. in Punjab (from panj-āb "five waters"). In archaic ablauting contractions, the laryngeal of the PIE root remains visible in Vedic Sanskrit, e.g. pratīpa- "against the current", from *proti-hxp-o-. In Tamil, Appu (Tamil form of "Ap") means water, and has references in poetry.
In the Rigveda, several hymns are dedicated to "the waters" (āpas): 7.49, 10.9, 10.30, 10.137. In the oldest of these, 7.49, the waters are connected with the drought of Indra. Agni, the god of fire, has a close association with water and is often referred to as Apām Napāt "offspring of the waters". In Vedic astrology, the female deity Apah is the presiding deity of the Purva Ashadhaasterism, meaning "first of the aṣāḍhā", with aṣāḍhā "the invincible one" being the name of the greater constellation.
The word has many cognates in archaic European toponyms, e.g., Mess-apia, and perhaps also Avon, from Old Brythonicabona or Welsh afon (pronounced [ˈavɔn]), both meaning 'river'.
Water 
Fire 
Aether 
Earth 
Sulphur 
Mercury
Salt 