When is water considered used, and does it become used merely by someone performing ablution (wudu’) with it, or is that restricted to water less than two Qullas? And what is meant by water that falls off or separates from the limbs of the one performing purification?

Used water is water that has separated from the limbs of one performing ablution (wudu) or ritual bath (ghusl). The apparent view of the madhhab is that it is pure (tahir) but not purifying (ghair mutahhir); it does not remove minor or major impurity (hadath) nor does it clean impurities (najasa). As for the remaining water from which a person performed ablution by scooping, it is not considered used and is deemed purifying.