How does one purify a water tank into which an animal has fallen?

Q 2: Small animals, such as cats, birds, and even snakes and rats, may fall into water reservoirs and tanks. How can we purify this water so that it can be used?

A: If animals that are unlawful to be eaten such as cats, snakes and the like or edible animals such as pigeons or chickens fall into the water but do not die, the water remains Tahir (ritually pure). If the animals die and the tank contains little water, it becomes Najis (ritually impure). However, if the tank is full of water and its taste, color, and smell does not change, it does not become Najis. It was related by Ahl-ul-Sunan (authors of Hadith compilations classified by jurisprudential themes) on the authority of Abu Sa`id (may Allah be pleased with him) that the Prophet (peace be upon him) said: When there is enough water to fill two pitchers, it bears no Najasah (ritual impurity). In another narration related by Ahmad, the Prophet (peace be upon him) said: When there is enough water to fill two pitchers, nothing will render it Najis. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.