Rabbi Akiva said: Happy is Israel before the One who purifies you. Who purifies you? Your Parent in Heaven. As it says, "I will sprinkle pure waters upon you and purify you" (Ezekiel 36: 25). And it says, "God is the hope (Mikveh) of Israel" (Jeremiah 17:13). Just as a mikveh purifies the ritually impure, so too does the Holy Blessed One purify Israel.

All seas are equivalent to a mikveh, for it is said, "And the gathering (ulemikveh) of the waters He called the seas" (Genesis 1:10), the words of Rabbi Meir. Rabbi Judah says: only the Great Sea is equivalent to a mikveh, for it says "seas" only because there are in it many kinds of seas. Rabbi Yose says: all seas afford cleanness when running, and yet they are unfit for zavim and metzoraim and for the preparation of the hatat waters.

If a wave was separated [from the sea] and was forty seahs, and it fell on a man or on vessels, they become clean. Any place containing forty seahs is valid for immersing oneself and for immersing other things. One may immerse in trenches or in ditches or even in a donkey-track whose water is connected in a valley. Bet Shammai say: one may immerse in a rain torrent. But Bet Hillel say: one may not immerse. They agree that one may block its flow with vessels and immerse oneself in it, but the vessels with which the flow is blocked are not thereby [validly] immersed.

If a mikveh contained forty seahs exactly and two persons went down and immersed themselves one after the other, the first becomes clean but the second remains unclean. Rabbi Judah says: if the feet of the first were still touching the water, the second also becomes clean. If one immersed a thick cloak and when he drew it out a part was still in contact with the water [and then another person immersed himself in the mikveh], he becomes clean. A pillow case or a cushion of leather, as soon as it is taken out of the water by its open ends the water which still remains in it is drawn water. How should one do it? One should immerse them and draw them up by their lower edges.

If he immersed a bed in it, even though its legs sink into the thick mud, it still becomes clean because the water touched them before [the mud]. The water of a mikveh which is shallow, one may press down even bundles of sticks, even bundles of reeds, so that the level of the water may rise, and then go down and immerse oneself. If an [unclean] needle is placed on the step [leading down to a mikveh] in a cavern, and the water is put in motion, once a wave has passed over it, [the needle] becomes clean.

The following block [immersion] in the case of a person: threads of wool, threads of flax and the ribbons on the heads of girls. Rabbi Judah says: those of wool or of hair do not interpose, because water enters through them.

The following do not block: the matted hair of the head and of the armpits and of a man's hidden parts. Rabbi Eliezer says: it is the same with a man or a woman: if it is something which one finds annoying, it blocks; but if it is something which one does not find annoying, it does not interpose.

There are six degrees of mikvaot, each superior to the other. The water of pools [smaller than 40 seah] if an unclean person drank of it and then a clean person drank of it, he becomes unclean; If an unclean person drank of it and then drew water from it in a clean vessel, [the vessel] becomes unclean; If an unclean person drank of it and then a loaf of terumah fell in: If he washed [his hands] in it, it becomes unclean; But if he did not wash [his hands] in it, it continues clean.

Superior to such [water] is the water of rain flows which have not stopped. If an unclean person drank of it and then a clean person drank of it, he is clean. If an unclean person drank of it and water was then drawn from it in a clean vessel, it is clean. If an unclean person drank of it and a loaf of terumah fell in, even if he washed his hand in it, it is clean. If one drew water from it in an unclean vessel and then a clean person drank [out of the pool], he is clean. If one drew water from it in an unclean vessel and a loaf of terumah fell [into the pool], even if he washed his hands in it, it is clean. If unclean water fell into it and a clean person drank of it, he is clean. If unclean water fell into it and one drew water from it in a clean vessel, it is clean. If unclean water fell into it and a loaf of terumah fell in, even if he washed his hands in it, it is clean. [All such water] is valid for terumah and for the washing of the hands.

Superior to such [water] is [the water of] the mikveh containing forty seahs, for in it people may immerse themselves and immerse other [things]. Superior to such [water] is [the water of] a spring whose own water is little but has been increased by a greater quantity of drawn water. It is equivalent to the mikveh in as much as it may render clean by standing water, and to an [ordinary] spring in as much as one may immerse in it whatever the quantity of its contents.

Superior to them are "smitten waters" which can purify even when flowing [on the ground]. Superior to them are "living waters" for in them there is immersion for zavim and sprinkling for metzoraim, and they are valid for the preparation of the hatat waters.