Hadath is the ritual state that necessitates wudu or ghusl before acts such as prayer. It is distinct from visible dirt or physical filth: a person can look clean while lacking wudu or being in janabah.
Using water to remove that ritual state triggers the juristic question of used water; ordinary removal of dust is a different matter.
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Used Water: Definition, Ruling and Juristic Differences
Hadath is the ritual state that necessitates wudu or ghusl before acts such as prayer. It is distinct from visible dirt or physical filth: a person can look clean while lacking wudu or being in janabah.
Using water to remove that ritual state triggers the juristic question of used water; ordinary removal of dust is a different matter.