وَالْمَاءُ الْمُسْتَعْمَلُ لَا يَجُوزُ اسْتِعْمَالُهُ فِي طَهَارَةِ الْأَحْدَاثِ.
Meaning: Used water may not be employed for purification from ritual impurity.
Purification from ritual impurity refers to the wudu or ghusl required for worship, not merely washing away dirt.
Within the Hanafi discussions, the classification of used water as intrinsically pure or impure is disputed; however, its inability to serve again for ritual purification is treated as the core rule.