What is the ruling on water used for ablution (wudu')—is it pure and purifying, and is it permissible to perform ablution with it? And what is the ruling on water that is touched by some water from a ritual bath (ghusl)?

The water used for ablution (wudu') is pure and purifying according to the majority of scholars, and it is permissible to use it whether it was water from which a person bathed or performed ablution. Scholars have agreed on the permissibility of a man and a woman performing wudu' and ghusl from the same vessel, and the permissibility of a man and a woman performing wudu' with the leftover water of a man, and the leftover water of a woman for a man, whether she was alone with it or not.

As for the water that separates from the limbs during wudu', it is pure according to the majority of scholars, but they differed on the permissibility of performing wudu' with it. Some of them disliked using it for purification if other water was available (like the Maliki school), while others, such as the Shafi'is and Hanbalis, said that it is not permissible to use it to remove ritual impurity despite its purity.

As for water that is touched by some water from ghusl, if the ghusl was for major ritual impurity (janabah) and only a small amount of water from it touched the other water, it is excused. However, if the amount was large, some jurists deemed it impermissible to purify oneself with it, while the water itself remains pure.