Chukát / vörös tehén gyakorlata

How is the water sanctified with the ashes of the red heifer? One should place the water that was drawn for this purpose in a container and then place ashes on the water so that they will be seen on the surface of the water. This is sufficient even though it is a large barrel filled with water. He should then mix the entire contents. If he placed the ashes in the container first and then placed the water upon them, it is disqualified.
What then is meant by the Torah's statement Numbers 19:17: "And he shall place living water upon it"? That the ash should be mixed with the water.

If they did not find the residue of the ashes of the seven [red cows] they performed the sprinkling with those of six, of five, of four, of three, of two or of one. And who prepared these? Moses prepared the first, Ezra prepared the second, and five were prepared from the time of Ezra, the words of Rabbi Meir. But the sages say: seven from the time of Ezra. And who prepared them? Shimon the Just and Yohanan the high priest prepared two each; Elihoenai the son of Ha-Kof and Hanamel the Egyptian and Ishmael the son of Piabi prepared one each.

§ The mishna states: He would take loose dust from underneath the tablet and place it into the vessel with the water, so that the dust would be visible upon the water. The Sages taught (Tosefta 1:8): Three items are required to be seen: The dust of the sota must be visible in the water, the ashes of the red heifer must be visible when placed in the waters of purification, and the spittle of a woman whose husband, who has a brother, died childless [yevama] must be visible. The yavam, brother-in-law of the yevama, is bound by Torah law to marry her, and this bond is dissolved through the ritual of ḥalitza, in which she spits before him in the presence of judges. In the name of Rabbi Yishmael they said: Even the blood of the bird used in a leper’s purification ritual is required to be visible in the vessel.

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[The priest] takes an earthenware bowl and pours half a log of water into it from the laver. Rabbi Judah says: a quarter [of a log]. Just as [Rabbi Judah] reduces the amount of writing, so he reduces the quantity of water. [Then the priest] enters the temple and turns to his right and there was a place there [on the floor] that was a cubit by a cubit, and a marble tablet, to which a ring was attached. When he would lift this up, he would take some dust from beneath it which he puts [into the bowl] so that it would be seen on top of the water; as it is said, “And of the dust that is on the floor of the Tabernacle the priest shall take, and put it into the water” (Numbers 5:17).

None of its ashes are brought into the Temple Courtyard for storage, as ibid.:9 states: "And he shall place it outside the camp." The ashes were divided into three portions: one was placed in the chayl, one on the Mount of Olives, and one was divided among all the priestly guardposts.
The one that was divided among all the priestly watches was used by the priests to sanctify themselves. The one that was placed on the Mount of Olives was used by the entire Jewish people for sprinkling. And the one that was placed in the chayl was prepared and hidden away, as implied by ibid. which states: "It will be a security for the congregation of Israel." This teaches that it was put away for safekeeping.
Indeed, in the chayl, they would put away for safekeeping a portion of the ashes from every red heifer that was burnt. Nine red heifers were offered from the time that they were commanded to fulfill this mitzvah until the time when the Temple was destroyed a second time. The first was brought by Moses our teacher. The second was brought by Ezra. Seven others were offered until the destruction of the Second Temple. And the tenth will be brought by the king Mashiach; may he speedily be revealed. Amen, so may it be G‑d's will.

If they did not find the residue of the ashes of the seven [red cows] they performed the sprinkling with those of six, of five, of four, of three, of two or of one. And who prepared these? Moses prepared the first, Ezra prepared the second, and five were prepared from the time of Ezra, the words of Rabbi Meir. But the sages say: seven from the time of Ezra. And who prepared them? Shimon the Just and Yohanan the high priest prepared two each; Elihoenai the son of Ha-Kof and Hanamel the Egyptian and Ishmael the son of Piabi prepared one each.