One is that it becomes impure only if its properties change. This is the position of Abū Hanīfah, despite his strictness concerning standing water. It is also Mālik’s position, al-Shāfiʿī’s earlier view, the more explicit of the two positions reported from Ahmad, and the view preferred by the discerning scholars among his followers. Al-Shāfiʿī’s other view, also reported from Ahmad, is that flowing water is treated like standing water, with each successive portion of the flow assessed separately.

The first view is correct. The Prophet, peace and blessings be upon him, distinguished between standing and flowing water when prohibiting bathing and urinating in standing water. This indicates a distinction between the two. Moreover, if impurity does not change flowing water, there is no basis for declaring it impure.

His statement,

“When water reaches two qullahs (large jars), it does not become impure,”

indicates the ruling concerning smaller quantities only by contrary implication, and such an implication has no universal scope. Thus, it does not establish that water below two qullahs necessarily becomes impure. Rather, the hadith is still given effect if a distinction is made between standing and flowing water, or if water below that quantity becomes impure in some circumstances.

Since the water is certainly pure, and neither a scriptural text nor analogy establishes its impurity, it must continue to be regarded as pure so long as its properties remain unchanged. According to the correct view, even a small quantity of water in an overflowing bathhouse basin does not become impure when urine, blood, or excrement falls into it without changing it. How much more, then, does this apply to water whose entire volume flows over the bathhouse floor? If impurity falls into it without changing it, it does not become impure.