I say, and with God's success: If the water that the dog comes into contact with is less than that which it does not come into contact with, it is permissible to perform ablution from it. However, if the water that the dog comes into contact with is more than that which it does not come into contact with, it is not permissible to perform ablution from 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.