Halacha

הלכה א
הַנּוֹגֵעַ בְּמֵי חַטָּאת שֶׁלֹּא לְצֹרֶךְ הַזָּאָה בֵּין אָדָם בֵּין כֵּלִים טָמֵא וְאֵינוֹ מְטַמֵּא בְּגָדִים בִּשְׁעַת מַגָּעוֹ. שֶׁנֶּאֱמַר (במדבר יט כא) "וְהַנֹּגֵעַ בְּמֵי הַנִּדָּה יִטְמָא עַד הָעָרֶב". הִנֵּה לָמַדְתָּ שֶׁמֵּי הַנִּדָּה אָב מֵאֲבוֹת הַטֻּמְאוֹת שֶׁל תּוֹרָה. וְטֻמְאַת מַגָּעָן בְּכָל שֶׁהוּא. וְאִם הָיָה בָּהֶן כְּדֵי הַזָּאָה מְטַמְּאִין בְּמַגָּע וּבְמַשָּׂא. וְהַנּוֹגֵעַ בָּהֶן אוֹ שֶׁנּוֹשְׂאָן שֶׁלֹּא לְצֹרֶךְ מְטַמֵּא בְּגָדִים בִּשְׁעַת מַגָּעוֹ אוֹ בִּשְׁעַת מַשָּׂאוֹ עַד שֶׁיִּפְרשׁ מִמְּטַמְּאָיו שֶׁנֶּאֱמַר (במדבר יט כא) "וּמַזֵּה מֵי הַנִּדָּה יְכַבֵּס בְּגָדָיו". אֵינוֹ מְדַבֵּר בְּמַזֶּה עַל הַטָּמֵא אִם טִהֵר אֶת הַטָּמֵא קַל וָחֹמֶר שֶׁיִּהְיֶה הוּא טָהוֹר. מִפִּי הַשְּׁמוּעָה לָמְדוּ שֶׁזֶּה שֶׁנֶּאֱמַר בַּתּוֹרָה וּמַזֵּה מֵי הַנִּדָּה לֹא נֶאֱמַר אֶלָּא לְשִׁעוּר שֶׁהַנּוֹגֵעַ אוֹ הַנּוֹשֵׂא מֵי נִדָּה שֶׁיֵּשׁ בָּהֶן כְּדֵי הַזָּיָה שֶׁלֹּא לְצֹרֶךְ הַזָּאָה טָמֵא וּמְטַמֵּא בְּגָדִים דִּין תּוֹרָה. וְכַמָּה הוּא שִׁעוּר הַזָּאָה כְּדֵי שֶׁיִּטְבּל רָאשֵׁי גִּבְעוֹלִין שֶׁל אֵזוֹב בְּמַיִם. בַּמֶּה דְּבָרִים אֲמוּרִים שֶׁמֵּי חַטָּאת מְטַמְּאִין בִּזְמַן שֶׁנָּגַע בָּהֶן אוֹ נְשָׂאָן שֶׁלֹּא לְצֹרֶךְ קֹדֶם שֶׁיַּעֲשׂוּ מִצְוָתָן. אֲבָל אַחַר שֶׁעָשׂוּ מִצְוָתָן אֵינָן מְטַמְּאִין כְּלָל. כֵּיצַד. הֲרֵי שֶׁטָּבַל אֶת הָאֵזוֹב וְהִזָּה עַל הָאָדָם הַטָּמֵא אוֹ עַל הַכֵּלִים וְהָיוּ הַמַּיִם שׁוֹתְתִין וְיוֹרְדִין מֵעַל הַטָּמֵא לָאָרֶץ. וְכֵן הַמַּיִם הַנִּתָּזִין בִּשְׁעַת הַזָּאָה עַל הָאָרֶץ אוֹ עַל הַטָּהוֹר הֲרֵי אוֹתָן הַמַּיִם טְהוֹרִים וְהַנּוֹגֵעַ בָּהֶן וְהַנּוֹשְׂאָן טָהוֹר. הִטְבִּיל אֶת הָאֵזוֹב לְהַזּוֹת עַל דָּבָר שֶׁאֵינוֹ מְקַבֵּל טֻמְאָה הֲרֵי הַמַּיִם הַמְנַטְּפִין כְּשֵׁרִין לְהַזּוֹת מֵהֶן כְּמוֹ שֶׁבֵּאַרְנוּ. לְפִיכָךְ מְטַמְּאִין טֻמְאַת מֵי חַטָּאת לְפִי שֶׁלֹּא עָשׂוּ מִצְוָתָן שֶׁהֲרֵי הַטְּבִילָה הָיְתָה לְשֵׁם דָּבָר שֶׁאֵינוֹ מְקַבֵּל טֻמְאָה:
כסף משנה
1.
Any person or article which touches sanctified water for a purpose other than sprinkling contracts impurity. The person does not impart impurity to his clothes, however, even when touching the water, as Numbers 19:21 states: "One who touches the sprinkling water will become impure until the evening." Thus it is derived that the sprinkling water is a primary source of impurity according to Scriptural Law and even the slightest amount of it imparts ritual impurity.
If there is enough water to sprinkle, it imparts impurity when touched and when carried and one who touches it or carries it for a purpose other than sprinkling imparts impurity to his clothes when touching it or carrying it until he separates himself from the source of his impurity, as implied by ibid. which states: "One who sprinkles the water shall launder his garments." Now this is not speaking about someone who sprinkles water on an impure person, for if he purifies an impure person, one can certainly infer that he himself remains pure. According to the Oral Tradition, it was taught that the Torah's statement "One who sprinkles the water shall launder his garments" was stated only to teach the measure that imparts impurity; i.e., that if one touches or carries a measure of sanctified water that could be sprinkled for an intent other than sprinkling, he is impure and he imparts impurity to his garments according to Scriptural Law.
How much is a measure of sprinkling? Enough to immerse the tops of the stalks of hyssop in the water.
When does the statement that the water for this purification imparts impurity apply? When one touched it or carried it for an intent other than sprinkling before they were used for their mitzvah. After they were used for their mitzvah, by contrast, they do not impart impurity at all.
What is implied? One immersed the hyssop in the sanctified water and sprinkled it on an impure person or keilim and the water was dripping and descending from the impure person to the ground or when he sprinkled the water, water was sprinkled on the ground or on a pure person, that water is pure and one who touches or carries it is pure.
If one immersed the hyssop to sprinkle water on an object that is not susceptible to ritual impurity, the water which drips from it is fit to be sprinkled again, as we explained. Therefore they impart the impurity of sanctified water to one who touches or carries them because they were not used for their mitzvah, for the immersion of the hyssop was for the intent of sprinkling on something that is not susceptible to ritual impurity.

הלכה ב
אֵין מֵי חַטָּאת מְטַמְּאִין אֶת הַכּל קֹדֶם שֶׁיַּעֲשׂוּ מִצְוָתָן עַד שֶׁיִּהְיוּ טְהוֹרִין וּכְשֵׁרִין לְהַזָּאָה. אֲבָל מֵי חַטָּאת שֶׁנִּפְסְלוּ כְּגוֹן שֶׁנִּתְעָרֵב בָּהֶן מַיִם אוֹ שֶׁשָּׁתְתָה מֵהֶן בְּהֵמָה וְכַיּוֹצֵא בָּהֶן מֵאֵלּוּ הַדְּבָרִים הַפּוֹסְלִין אוֹתָן אִם נָגַע בָּהֶן הַטָּהוֹר לִתְרוּמָה נִטְמָא בֵּין שֶׁנָּגַע בְּיָדָיו בֵּין שֶׁנָּגַע בִּשְׁאָר גּוּפוֹ. נָגַע בָּהֶן אָדָם הַטָּהוֹר לְחַטָּאת וַאֲפִלּוּ בְּיָדָיו הֲרֵי הוּא טָהוֹר כְּמוֹת שֶׁהָיוּ:
כסף משנה
2.
The water for the purification process involving the ashes of the red heifer does not impart impurity to anything before its mitzvah is performed unless it is pure and acceptable to be used for sprinkling. Different rules apply, however, if this water was disqualified - e.g., other water was mixed with it, an animal drank from it, or other factors that disqualify it arose. If a person who is pure with regard to terumah touches it, he contracts impurity whether he touches it with his hand or with other parts of his body. If a person who is pure with regard to this purification process touches it, even with his hand, he remains pure, as he was originally.

הלכה ג
מֵי חַטָּאת שֶׁנִּטְמְאוּ וְנָגַע בָּהֶן אַחַר שֶׁנִּטְמְאוּ אָדָם הַטָּהוֹר לִתְרוּמָה בֵּין בְּיָדָיו בֵּין בְּגוּפוֹ נִטְמָא. וְאִם נָגַע בָּהֶן הַטָּהוֹר לְחַטָּאת בְּיָדָיו נִטְמָא. נָגַע בִּשְׁאָר גּוּפוֹ הֲרֵי הוּא טָהוֹר כְּמוֹת שֶׁהָיָה:
כסף משנה
3.
If sanctified water contracted impurity and a person who was pure with regard to terumah touched it, whether with his hands or with his body, after it contracted impurity, he contracts impurity. If a person who had purified himself for this purification process touches it with his hands, he contracts impurity. If he touches it with the remainder of his body, he remains pure, as he was originally.

הלכה ד
מֵי חַטָּאת שֶׁנָּפְלוּ לְתוֹכָן מֵי מַעְיָן אוֹ מֵי מִקְוֶה אוֹ מֵי פֵּרוֹת. אִם רֹב מֵי חַטָּאת מְטַמְּאִין בְּמַשָּׂא. וְאִם רֹב מֵי פֵּרוֹת אֵין מְטַמְּאִין. מֶחֱצָה לְמֶחֱצָה מְטַמְּאִין. אֵפֶר פָּרָה שֶׁנִּתְעָרֵב בְּאֵפֶר מַקְלֶה וְקִדֵּשׁ בְּכֻלָּן אִם הָיָה הָרֹב אֵפֶר פָּרָה מְטַמְּאִין בְּמֵי נִדָּה. וְאִם הָיָה הָרֹב אֵפֶר מַקְלֶה אֵין מְטַמְּאִין בְּמַגָּע אֲבָל מְטַמְּאִין בְּמַשָּׂא:
כסף משנה
4.
The following rules apply if water from a spring, a mikveh, or fruit juice falls into sanctified water. If the majority is sanctified water, the mixture imparts impurity when carried. If the majority is fruit juice, it does not impart impurity. If it is half and half, it imparts impurity.
The following laws apply if the ashes of the red heifer become mixed with ashes from an oven and a person sanctified water with the entire mixture. If the majority of the mixture are the ashes of the red heifer, the water imparts impurity like sanctified water. If the majority are oven ashes, the water does not impart impurity when touched, but does impart impurity when carried.

הלכה ה
אֵפֶר כָּשֵׁר שֶׁנְּתָנוֹ עַל גַּבֵּי הַמַּיִם שֶׁאֵינָן רְאוּיִין לְקַדְּשָׁן וְנָגַע בָּהֶן הַטָּהוֹר לִתְרוּמָה בֵּין בְּיָדָיו בֵּין בְּגוּפוֹ נִטְמָא. נָגַע בָּהֶן הַטָּהוֹר לְחַטָּאת אֲפִלּוּ בְּיָדָיו הֲרֵי זֶה טָהוֹר כְּמוֹת שֶׁהָיָה:
כסף משנה
5.
When acceptable ashes were sprinkled on water that was not fit to be sanctified and then a person who was pure with regard to terumah touched the water with his hands or with his body, he contracts impurity. If a person who purified himself for this purification process touched such water, even with his hands, he remains pure, as he was originally.

הלכה ו
מֵי חַטָּאת שֶׁנִּפְסְלוּ לֹא יְגַבְּלֵם בְּטִיט שֶׁלֹּא יַעֲשֵׂם תַּקָּלָה לַאֲחֵרִים שֶׁמָּא יִגַּע בַּטִּיט וִיטַמֵּא. שֶׁמֵּי חַטָּאת אֵינָם בְּטֵלִין בְּטִיט שֶׁנֶּאֱמַר (במדבר יט ט) "חַטָּאת הִיא":
כסף משנה
6.
When sanctified water is disqualified, it should not be mixed with mud, so as not to create a stumbling block for others, lest they touch the mud and become impure. For the sanctified water does not become nullified in the mud, as implied by Numbers 19:9: "It is a sin-offering."

הלכה ז
פָּרָה שֶׁשָּׁתָת מֵי חַטָּאת אַף עַל פִּי שֶׁנִּשְׁחֲטָה בְּתוֹךְ כ''ד שָׁעוֹת בְּשָׂרָהּ טָהוֹר שֶׁנֶּאֱמַר (במדבר יט ט) "לְמִשְׁמֶרֶת לְמֵי נִדָּה". בִּזְמַן שֶׁהֵן שְׁמוּרִין אֵינָן בְּטֵלִין. אֲבָל בִּזְמַן שֶׁשְּׁתָאָתָן פָּרָה בָּטְלוּ שֶׁהֲרֵי אֵינָם שְׁמוּרִין:
כסף משנה
7.
When a cow drinks from sanctified water, its meat is pure even if it was slaughtered within 24 hours of drinking, as can be inferred from ibid.: "as safekeeping, as water for sprinkling." Implied is that when the water is kept safe, it is not nullified. If, however, a cow drank from it, it is nullified, because it was not kept safe.

הלכה ח
הַמַּזֶּה מֵחַלּוֹן שֶׁמַּזִּין מִמֶּנּוּ עַל הָרַבִּים. וְהֻזָּה עָלָיו וְנִכְנַס לַמִּקְדָּשׁ וְאַחַר כָּךְ נִמְצְאוּ הַמַּיִם פְּסוּלִין הֲרֵי זֶה פָּטוּר. שֶׁחֶזְקַת הַמַּיִם שֶׁמַּזִּין מֵהֶן עַל הָרַבִּים שֶׁהֵן כְּשֵׁרִין וַהֲרֵי זֶה כְּאָנוּס. אֲבָל אִם הֻזָּה עָלָיו מֵחַלּוֹן שֶׁל יָחִיד וְנִכְנַס לַמִּקְדָּשׁ וְנִמְצְאוּ הַמַּיִם פְּסוּלִין חַיָּב בְּקָרְבָּן עוֹלֶה וְיוֹרֵד מִפְּנֵי שֶׁהָיָה לוֹ לִבְדֹּק עַל הַמַּיִם וְאַחַר כָּךְ יִכָּנֵס לַמִּקְדָּשׁ. מַחֲלִיקִים הָיוּ הָעָם בַּמַּיִם שֶׁשּׁוֹתְתִים בָּאָרֶץ מֵחַלּוֹן שֶׁל רַבִּים וְדוֹרְסִים אוֹתָן וְנִכְנָסִים לַמִּקְדָּשׁ וְלֹא הָיוּ חוֹשְׁשִׁין לָהֶן שֶׁמָּא פְּסוּלִין הֵן:
כסף משנה
8.
When water is sprinkled on a person from a window from which water is sprinkled on many individuals, he entered the Temple, and then it is discovered that the water was disqualified, he is exempt. The rationale is that one can assume that the water that is sprinkled on many people is acceptable. Hence, he is considered as one who transgressed because of factors beyond his control.
If, however, water was sprinkled on a person from the window of a private individual and he entered the Temple and afterwards, it was discovered that the water was disqualified, he is obligated to bring an adjustable guilt-offering. The rationale is that he should have investigated the status of the water and only afterwards, entered the Temple.
Even if people would slip on water that had been sprinkled from a window from which water is sprinkled on many individuals and was flowing on the ground and they would tread on it, they would enter the Temple without being concerned that they had been disqualified.

הלכה ט
הַמַּזֶּה בְּאֵזוֹב הַטָּמֵא לְחַטָּאת. אִם יֵשׁ בּוֹ כְּבֵיצָה הַמַּיִם פְּסוּלִין וְהַזָּיָתוֹ [פְּסוּלָה]. אֵין בּוֹ כְּבֵיצָה הַמַּיִם כְּשֵׁרִים וְהַזָּאָתוֹ פְּסוּלָה. וְאֵזוֹב זֶה מְטַמֵּא חֲבֵרוֹ וַחֲבֵרוֹ לַחֲבֵרוֹ אֲפִלּוּ הֵן מֵאָה שֶׁאֵין מוֹנִין לְחַטָּאת:
כסף משנה
9.
When a person sprinkles such water, using a hyssop that is impure with regard to this sacrificial process, if it is the size of an egg, the water is impure and the sprinkling is unacceptable. If it is less than the size of an egg, the water is pure, but the sprinkling is unacceptable. This hyssop can impart impurity to another, and that other, to still another, even when the chain reaches 100, because levels of impurity are not counted with regard to the purification process involving the ashes of the red heifer.

הלכה י
הַמַּגְבִּיהַּ כְּלִי שֶׁהֻזָּה עָלָיו וַהֲרֵי עָלָיו הַמַּיִם כְּדֵי הַזָּאָה טָהוֹר שֶׁהַמַּיִם שֶׁעָשׂוּ מִצְוָתָן אֵינָן מְטַמְּאִין כְּמוֹ שֶׁבֵּאַרְנוּ: בְּרִיךְ רַחֲמָנָא דְּסַיְּעָן
כסף משנה
10.
When a person lifts up a k'li upon which this water has been sprinkled and enough water to be sprinkled remains upon it, he is pure. Once the water has performed its mitzvah, it does not impart impurity, as we explained.

טהרה הלכות פרה אדומה פרק טו
Taharah Para Aduma Chapter 15