וְלָֽקְחוּ֙ לַטָּמֵ֔א מֵעֲפַ֖ר שְׂרֵפַ֣ת הַֽחַטָּ֑את וְנָתַ֥ן עָלָ֛יו מַ֥יִם חַיִּ֖ים אֶל־כֶּֽלִי׃
E per gli impuri essi prenderanno le ceneri del fuoco della purificazione dal peccato e l'acqua corrente sarà messa in una nave.
Mishnah Mikvaot
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.
Mishnah Mikvaot
[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.