Purifying (ṭahūr) water is that which is pure in itself and purifies other things. It remains upon its original creation—that is, the natural state in which it was made—whether it descends from the sky, like rain, melted snow, and hail; flows upon the earth, such as the waters of rivers, springs, wells, and seas; or is obtained by distillation.

This alone is the water with which it is valid to remove ritual impurity and physical defilement. If it is altered by something impure, using it for purification is not permitted, and there is no disagreement about this. If, on the other hand, it is altered by a pure substance that does not dominate it, the sounder of the two scholarly opinions is that it may still be used for purification.

Shaykh al-Islam Ibn Taymiyyah said: “With regard to the question of a small or large amount of water being changed by pure substances—such as ishnān (alkali), soap, sidr (lote leaves), khatmī (marsh mallow), earth, dough, and so forth—so that the water is affected, as in a vessel that still contains traces of sidr or khatmī and water is poured into it, changing while the designation ‘water’ still applies, there are two well-known opinions among the scholars.”

He then set them out, discussed the evidence for each, and gave preference to the view that purification with such water is valid. He said: “This is the correct position, because Allah, exalted is He, says: ‘If you are ill, or on a journey, or one of you comes from answering the call of nature, or you have touched women and you cannot find water, then perform tayammum with clean earth and wipe your faces and hands with it’ (Q 4:43). The words ‘you cannot find water’ are an indefinite noun in a context of negation, and therefore they include everything that comes under the name ‘water,’ with no distinction between one kind and another.” End quote.

Accordingly, when water is absent, or a person is unable to use it even though it is available, Allah has made