[Water from] a spring which is made to pass over into a trough becomes invalid. If it was made to pass over the edge in any quantity, [what is] outside [the trough] is valid, for [the water of] a spring purifies however little its quantity. If it is made to pass over into a pool and then is stopped, the pool counts as a mikveh. If it is made to flow again, it is invalid for zavim and for those with skin disease and for the preparation of the hatat waters until it is known that the former [water] is gone.

If it was made to pass over the outside of vessels or over a bench: Rabbi Judah says: behold it remains as it was before. Rabbi Yose says: behold it is like a mikveh, except that one may not immerse anything above the bench.

If [water from] a spring that flows into many channels was increased in quantity so that it was made to flow in abundance, it remains as it was before. If it was standing and its quantity was increased so that it was made to flow, it becomes equal to a mikveh in that it can purify in standing water, and to a spring in that one may immerse [objects] therein however small its quantity.

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.

Flowing water is considered like a spring and dripping water is considered like a mikveh. Rabbi Zadok testified that if flowing water exceeded dripping water [with which it was mixed] it was valid [as flowing water]. If dripping water became flowing water, its flow may be blocked by a stick or by a reed or even by a zav or a zavah, and then one may go down and immerse oneself in it, the words of Rabbi Judah. Rabbi Yose says: one may not stop the flow of water with anything which is liable to uncleanness.

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.