The water in which a person who is in a state of ritual impurity has immersed himself can only be used from what has fallen from the limbs or has touched the body. In comparison to the rest of the water, it is considered little. Therefore, it is permissible to perform ablution and bathing with it; because the water that has mixed with used water is judged by the predominance of weight, and here the used water is little compared to the rest of the water. Refer to: Al-Ikhtiyar, 1/20, Al-Lubab, 1/18-19, Al-Hadiyyah Al-Alaiyyah, pp. 39-40, and Allah knows best.