What is a small amount of water and what is a large amount of water?

The small amount of water according to the Hanbalis and Shafi'is is what is less than two Qullas, which is approximately 200 liters. If impurity falls into it, it becomes impure. As for the Malikis, a small amount of water is what is equivalent to a vessel used for ablution (wudu') or ritual bath (ghusl). The term "difficult water" (al-ma' al-'asir) was not mentioned in the discourse of the scholars; rather, the opposite of a small amount of water is a large amount of water.