The Spanish word 'agua' meaning 'water' comes directly from the Latin word 'aqua', which also meant 'water'. The change from Latin 'qu' to Spanish 'gu' is a common sound change that occurred as Latin evolved into Spanish, making the word easier to pronounce while maintaining its essential meaning.

Several common Spanish words are derived from the same Latin root 'aqua', including: 'acuático' (aquatic), 'acuoso' (watery), and 'aguacero' (downpour). The connection to water is clear in all these related terms.

Many English words are related to 'agua' through the same Latin ancestor 'aqua'. Some common examples include 'aquarium' (a container for water and aquatic life), 'aquatic' (relating to water), and 'aqueduct' (a water channel). Even words like 'aqueous' (watery) and 'aquifer' (underground layer of water-bearing rock) share this connection. The Latin 'aqua' is so directly preserved in English that we still use it in phrases like 'aqua blue' to describe a water-like blue color.