From Proto-Italic *akʷā, from Proto-Indo-European *h₂ékʷeh₂. Cognate with Proto-Germanic *ahwō (“water, stream”).
The few cognates in other Indo-European branches point to a narrower original meaning of "running water". See Umbrian 𐌖𐌕𐌖𐌓 (utur, “water”), which instead represents a remnant Italic continuation of Proto-Indo-European *wódr̥, the more widespread word for water in Indo-European languages.