Source: Fatāwā Shaykh al-Ḥadīth Mubārakpūrī, Vol. 1, p. 179
Question:
Is it permissible to perform wuḍū with leftover (jootha) water?
Is it permissible to use the remaining water of istinjāʾ (used for cleansing after relieving oneself) for wuḍū or istinjāʾ?
Answer:
Al-ḥamdu lillāh, waṣ-ṣalātu wa-s-salāmu ʿalā Rasūlillāh, ammā baʿd!
◈ In both cases, namely:
- Performing wuḍū with leftover (jootha) water
- Performing wuḍū or istinjāʾ with water left after istinjāʾ
— there is no Sharʿī prohibition or dislike established from any authentic evidence.
◈ Many ideas and notions regarding these matters circulate among the common people without any foundation in Sharīʿah.
Conclusion:
✔ Performing wuḍū with leftover (jootha) water is permissible.
✔ Using the remaining water of wuḍū for istinjāʾ is also permissible.
ھذا ما عندي والله أعلم بالصواب