the scholars of knowledge—holds that water becomes impure only when it changes, without qualification, whether it reaches two qullahs or not. However, if it is less than two qullahs, one must take care when impurity falls into it, because water below that amount will generally undergo a change.
This is the correct view, both on the basis of the textual evidence and reasoned consideration.
As for the textual evidence, it is the Prophet’s ﷺ statement: “Water is purifying; nothing renders it impure.” What is excluded from this is water altered by an impurity, for it is impure by consensus. There is also an indication of this in the Quran. Allah Most High says:
“Forbidden to you are carrion, blood, the flesh of swine, and that which has been dedicated to other than Allah.” [al-Ma'idah 5:3]
And Allah Most High says:
“Say: I do not find, in what has been revealed to me, anything forbidden for one who wishes to eat it, unless it be carrion, spilled blood, or the flesh of swine—for indeed it is filth.” [al-An'am 6:145]
His words, “for indeed it is filth,” given as the reason for the ruling, show that whenever the state of filth is present, the ruling applies; and whenever it is absent, the ruling no longer applies. If this is so with regard to food, then the same applies to water.
For example, if spilled blood falls into water and affects it, the water becomes filthy and impure; but if it does not affect it, it is not so.
From the standpoint of reasoned consideration, the Sacred Law is wise and assigns rulings on the basis of effective causes, some of which are known to us and others unknown. The effective cause of impurity is filth. Whenever filth is present in something, it is impure; and whenever it is not present, it is not impure. Thus, the ruling revolves around its effective cause, being present when it is present and absent when it is absent.
If someone were to say: Among impurities are those whose color does not differ from that of water, such as urine, whose color at times may be the same as that of water.