If it is said: The Law has explicitly stated the impurity of a small amount of water, in his (peace and blessings of Allah be upon him) statement: "When water reaches two qullahs, it does not carry impurity."

We say: This is an argument for its purity, because the water of the conduit, in its entirety, has reached two qullahs, so it does not carry impurity. Specifying a particular 'flow' from it with this measure is an arbitrary assertion for which there is no evidence. Furthermore, the report was specifically regarding stagnant water, and it is not valid to analogize flowing water to it, due to its strength via its flow and connection to its source. Moreover, the report indicates, through its explicit wording (mantuq), the negation of impurity from that which has reached two qullahs, and one only argues here by its implication (mafhum). The requirement of the implication is satisfied by the difference between that which is less than two qullahs and that which has reached them. This difference has been achieved by the fact that for water less than two qullahs, flowing and stagnant water differ regarding impurity, whereas for that which has reached them, they do not differ. This is sufficient.

Al-Qadi and his companions said: Every 'flow' (jiryah) of flowing water is considered independently. If the impurity is flowing with the water, then what is in front of it is pure because the impurity has not reached it, and what is behind it is pure because it has not reached it. The 'flow' containing the impurity, if it reaches two qullahs, is pure unless it is altered by the impurity; if it is less than two qullahs, it is impure. If the impurity is stationary on the side of the river, its bed, or in a depression (wahdah) within it, then every 'flow' that passes over it, if it is less than two qullahs, is impure, and if it is two qullahs, it is pure, unless it is altered.

The 'flow' (jiryah) is the water containing the impurity, along with what is near it from behind and in front—that which it is customary to spread to, if it is of the type that spreads—along with all that is adjacent to that from between the two banks of the river. If the impurity is extended, every part of it has the same 'flow' considered for a small amount of impurity; all that is adjacent to it is not treated as a single 'flow', so as not to lead to rendering a large amount of water impure by a small amount of impurity, or to the negation of impurity from a large amount while significant impurity exists. For that which is adjacent to a large amount of impurity is a large amount of water, so it does not become impure, while that which is adjacent to a small amount of impurity is a small amount of water, so it becomes impure.