All impure entities - whether humans or keilim, whether they contracted a severe impurity of Scriptural origin or whether they contracted Rabbinic impurity - regain purity only through immersion in water that is collected in a pool in the ground.
Whenever the Torah mentions washing one's flesh or laundering one's garments from impurity, the intent is solely the immersion of the entire body or article in a mikveh. The phrase, Leviticus 15:11: "And he did not wash his hands in water," also refers to the immersion of the entire body. This also applies to other impure people. If one immersed himself entirely with the exception of the tip of his little finger, he is still ritually impure. Although all of these matters have their source in the Oral Tradition, Leviticus 11:32 does state: "He shall enter water; he remains impure until the evening and then he becomes pure." This rule is then applied with regard to all those impure: They must enter water.
All keilim that contract impurity can be purified through immersion in a mikveh with the exception of an earthenware container, a glass k'li, and a reed mat. With regard to an earthenware container, Leviticus 11:33 states: "You shall break it," implying that its purification comes only through breaking it. Even if it was joined to the earth, even affixed to it with a nail, and even if it was filled with lime or gypsum, it retains its impurity until it is broken. Our Sages considered glass keilim like earthenware containers in this respect.
A reed mat is not included among the keilim that are susceptible to other types of impurity. Since it does not have a receptacle, it is not in the category of the wooden keilim mentioned by the Torah. Nevertheless, since it is fit to lie upon, it was included among the keilim susceptible to midras impurity according to Scriptural Law. Now since there is no explicit mention of its association with purity and impurity in the Torah and yet, it was included among the articles that contract impurity, it was not included with regard to purification through immersion in a mikveh. For only keilim mentioned in the Torah can be purified in a mikveh. A reed mat can be purified only by being torn to the extent that there remain less than six handbreadths by six handbreadths.
A zav can be purified only through immersion in a stream, for Leviticus 15:13 states that he must immerse "in living water." A zavah and other persons and keilim that are impure may immerse or be immersed in a mikveh.
💧 Universal Purification
All impure persons and keilim regain purity only through immersion in collected water. Biblical phrases like 'washing his flesh' always refer to full-body immersion in a mikveh. Exceptions: earthenware vessels are broken, not immersed; a zav specifically requires 'living water.'
All those obligated to immerse may immerse during the day with the exception of a nidah and a woman after childbirth. They must immerse at night, as we explained with regard to the laws of nidah. One who has a seminal emission may immerse throughout the entire day from the beginning of the night. This is derived from Deuteronomy 23:12 which states: "And it shall be that toward evening, he shall immerse in water." This teaches that he may immerse and continue in his state from the beginning of the night until the night falls the following day.
All those who immerse should immerse their entire bodies while naked at one time. If the person has hair, all of his hair must be immersed; it is considered as part of his body according to Scriptural Law. Whenever impure individuals immersed while wearing clothes, the immersion is acceptable, because the water passes through the clothes and they do not intervene. Similarly, if a nidah immerses in her clothes, she is permitted to resume relations with her husband.
All those who immerse must have the intent to purify themselves through immersion. If one did not have such an intent, the immersion is acceptable with regard to ordinary foods. Even a nidah who immerses without intent, e.g., she fell into water or descended into water to cool off, is permitted to her husband. Nevertheless, with regard to terumah and sacrificial food, she is not considered pure until she immerses with the proper intent.
When a person ties his hands and feet and is seated in an irrigation canal, if the water covers his body entirely, he is pure. When a person jumps into a mikveh, it is reprehensible. When one immerses in a mikveh twice, it is reprehensible. When one tells a friend: "Place your hand upon me in the mikveh," it is reprehensible.
Water from the mikveh need not seep into the non-visible portions or the creases of a person's body, as implied by the verse: "And he did not wash his hands in water." It can be inferred that it is necessary only that visible portions of the body be in contact with the water. Nevertheless, the non-visible portions must be fit for water to reach them without there being any intervening substances upon them. Therefore, our Sages instructed: At home, a person should always teach that a woman should rinse between the folds of her body and then immerse. A woman should immerse as she stands normally when weaving or when nursing her child.
🕰️ Timing and Technique
Most immersions occur by day; a nidah and woman after childbirth must immerse at night. The entire body must be immersed naked at one time, including all hair. Intent to purify is required for terumah and sacred items, though lack of intent still permits ordinary foods. Water need not seep into hidden creases.
A woman should not immerse in a harbor, because she will be embarrassed because of the inhabitants of the city and will not immerse properly. If mats were erected as a screen for the purpose of modesty, she may immerse in a harbor. A woman should not immerse while standing on an earthenware container, on a basket, or the like, because she will be afraid of falling and the immersion will not be acceptable.
When either a human or a k'li is immersed, there should not be any intervening substance between them and the water. If there is an any intervening substance between them and the water - for example, there was dough or mud clinging to the flesh of a person or the substance of a k'li - the person or the k'li is impure as it was originally and the immersion is invaild. According to Scriptural Law, if there is an intervening substance covering the larger portion of the person's body or the larger portion of the k'li, the immersion is invalid, provided he objects to the intervening substance and would like to remove it. If, however, he does not object to it and does not pay attention whether it would be removed or not, it is not considered an intervening substance, even if it covers the major portion of the person or the k'li. Similarly, if it covers less than half a person's body, it is not considered as an intervening substance even if he objects to it. According to Rabbinic decree, any intervening substance that one objects to invalidates an immersion even if it covers only the lesser portion of the person's body. This is a decree, lest such a substance cover the greater portion of the person's body. And any intervening substance that covers the larger portion of the person's body disqualifies the immersion even if he does not object to it. This is a decree, lest a substance that one objects to cover the greater portion of his body. Thus if even a drop the size of a mustard seed of an intervening substance, e.g., dough, tar, or the like, was on a person's flesh or on the substance of a k'li, and he objects to it, his immersion is disqualified. If he does not object to it, the immersion is acceptable unless the intervening substance covers the major portion of the k'li or the person, as explained.
🚿 No Interpositions
A woman may not immerse in a harbor without a modesty screen, as embarrassment causes improper immersion. Any intervening substance — dough, mud, tar — between the body or vessel and the water invalidates the immersion.
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🎓 Key Principles
Chapter 1
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Water as the Universal Purifier All impure entities, human or vessels, return to purity exclusively through immersion in properly collected water.
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Biblical Washing Means Full Immersion Every Torah reference to 'washing flesh' or 'laundering garments' in purity contexts means complete immersion of the entire body or article.
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Intent Determines the Level of Purity Immersion without conscious intent is valid only for ordinary foods; higher purity levels such as terumah require deliberate intent to purify.
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Total Bodily Contact Required The entire body — every hair and every visible surface — must be simultaneously exposed to the water for the immersion to be valid.