The compound noun 'water-quality' is a modern English formation, combining two ancient roots to specify a distinct environmental concept. The first element, 'water', originates from the Proto-Indo-European root wodr̥-/wed-, meaning 'water' or 'wet', which evolved into the Old English wæter. The second element, 'quality', descends from the Latin qualitas, derived from qualis ('of what kind'), which itself relates to the interrogative stem kwo- seen in English 'what'. The literal combination, 'the kind/character of water', directly and logically yields the contemporary technical meaning, referring to the measurable properties that determine water's fitness for use in drinking, industry, or ecosystem health.

Structure: water (liquid) + quality (characteristic) water: From Old English wæter, of Proto-Germanic origin; related to Dutch water and German Wasser. Functions as the primary noun denoting the substance. quality: From Latin qualitas, from qualis 'of what kind'. Functions as a noun-forming suffix indicating a property or attribute.