What is the ruling if impurity is in the still water that is less than two qullahs, when meeting the flowing water?
Chapter on what purification is achieved with regarding water
Al-Mughni
Book of Purification
Primary text
If the impurity is in the still water, it never becomes impure. If the still water is less than two qullahs, and the flowing water is likewise less than two qullahs, but their combined volume exceeds two qullahs, and the impurity is in the still water, neither body becomes impure because the aggregate volume exceeds two qullahs.
Supporting text
If the impurity is in the flowing water, the apparent opinion of our associates dictates that the still water and the contaminated flowing portion become impure, as does whatever flows past the still water thereafter. This is because the flowing portion containing impurity was already impure before meeting the still water; the still water then became impure because it was less than two qullahs and received impure water. The flowing water does not become pure because it is analogous to impure water poured onto water less than two qullahs.