If a person performs wudu with a can of water and there is water remaining in that can, is he permitted to perform istinja (removal of filth) with the remaining water? Can wudu be performed with the remaining water and is it acceptable for him to throw away the remaining water?
Throwing away the water is considered a waste therefore Shariah rules it to be totally unlawful, and to use it for wudu is perfectly fine. However, it will be impermissible to use ther remaining water for wudu, if used water has fallen into it, to the extent that it exceeds the amount of unused water. With regards to Istinja there is no doubt to it being permissible to use, though with the glory and respect of Shariah in view, it is better that it be used for wudu.
It is stated in Durr al-Mukhtar: One should drink the remaining water of wudu whilst standing up and facing the Qibla. The left over water is similar (in virtue) to the water of Zamzam
It is stated in Tirmizi that Hazrat Ali drank the left over water of wudu whilst he was standing and then announced; “I wanted to let you know of the way, in which the Holy Prophet ﷺ performed wudu”.
It is stated in Radd al-Mukhtar that the water of Zamzam is a cure for illnesses and so is the left over water of wudu. Allama Abdul Ghani Nablusi states: “Whenever I am ill, I make the intention to drink the left over water of wudu, and by simply making the intention, I am cured from the illness. By having faith in the truthful words of the honest Prophet Muhammad ﷺ I have adapted this way of gaining remedy from any illness”.
And Allah ﷻ knows the best
Imam Ahmad Rida Khan رحمة الله تعالى عليه
Translation by Dr Musharraf Hussain Al-Azhari Translator of Majestic Quran, www.majesticquran.co.uk