«وَلَكِنْ يُرِيدُ لِيُطَهِّرَكُمْ»
But God intends to purify you.
For ritual purification, the mere linguistic existence of “water” is not enough: the substance must be capable of producing ritual purity. Impure water does not fulfill that purpose, even if ordinary language still calls it water.
Thus water altered by a pure additive and water rendered impure by contamination belong to different legal analyses. The purification requirement is grounded in the governing scriptural purpose, not an arbitrary extra preference.