وَتَجُوزُ الطَّهَارَةُ بِمَاءٍ خَالَطَهُ شَيْءٌ طَاهِرٌ فَغَيَّرَ أَحَدَ أَوْصَافِهِ
Meaning: Purification is permissible with water mixed with a clean substance that alters one of its properties.
Awṣāf refers to observable properties such as colour, smell and taste.
A slight change caused by a clean additive does not necessarily remove the substance’s identity as water.