Fiqh-us-Sunnah Volume 1, Purification and Prayer, Fiqh 1.006A.

Section : Water left in a pot after a pig or dog has drunk from it.

Such water is considered impure and must be avoided. Al-Bukhari and Muslim have recorded, on the authority of Abu Hurairah, that the messenger of Allah said, “If a dog drinks from one of your containers, wash it seven times.” Ahmad and Muslim also have this addition, “Cleanse one of your containers if a dog licks it by washing it seven times, the first washing being with dirt.” As for the leftover water of a pig, it is clearly considered filth and impure.