Watermelon juice differs from pure water only in taste. If this characteristic appears in it, it becomes pure but not purifying for ritual impurity. It is permissible to remove actual impurity with it, but it is not permissible to perform ablution or bathing with it. Refer to: Maraki al-Falah, pp. 26-27, and the commentary of al-Tahawi on Maraki, pp. 19-20, and Bada'i al-Sana'i, 1/16, and Al-Ikhtiyar, 1/20, and Al-Lubab, 1/18-19, and Al-Hadiyya al-Alaiyya, pp. 39-40.