I say, and with God's success: If the water is such that if a brick or a leaf is placed in it, it would be carried away, it is permissible to perform ablution with it; because it is flowing water, and flowing water does not become impure by the occurrence of impurity in it, unless one sees the effect of the impurity in the change of its taste, color, or smell, in which case it is not permissible to perform ablution with it. Refer to: Sharh al-Wiqayah p. 97, Ghinayat al-Mustamli 1: 819, Al-Bada'i 1: 71, and Fatwas of Qadi Khan 1: 4, and God knows best.