Question 108: What makes Ghusl (ritual bath) obligatory for a Muslim? How is Ghusl performed? Is it a must that no waste water from Ghusl should touch the clean water which is being used for Ghusl? What is the ruling if they touch each other; can a person proceed with Ghusl?
Answer: Amongst things which make it obligatory for a Muslim to make Ghusl is the emission of Maniy (sperm/vaginal secretions) during sleep; penetration of the glans penis into the vulva, even without ejaculating; and ejaculating Maniy in wakefulness accompanied by a feeling of pleasure, even without having sexual intercourse. Menstruation and postpartum period also make it obligatory on women to perform Ghusl once the bleeding stops. Besides, in case a spray of waste water from the Ghusl mixes with clean water which is being used for Ghusl; a person may proceed making Ghusl from it... read more here.