I say, with Allah's guidance: Flowing water — which is water that can carry a straw or a leaf — does not become impure by the falling of impurity into it, whether it is a little or a lot, as long as it is flowing, unless the effect of the impurity is seen in it by changing its taste, color, or smell; because the impurity does not settle in it with the flow of water, unlike stagnant water; and because the Prophet (peace be upon him) prohibited urinating in stagnant water, indicating a different ruling for flowing water. The Prophet (peace be upon him) said: 'Allah created water pure, nothing makes it impure, except what changes its taste,' which is applicable to flowing water. See: Sharh al-Wiqayah, p. 96, and Allah knows best.