What is the ruling when multiple flowing streams ('jariyat') converge?

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If the confluence is changed by impurity, all the collected water is impure, regardless of its volume. If there is a continuous flow of pure water in some of the streams that reaches two qullahs, either initially or subsequently, the entirety is pure, provided it has not changed. This is because the two-qullah volume repels impurity from itself and from what it joins.