Reference for Mikvaot 1:8
לְמַעְלָה מֵהֶן, מַיִם מֻכִּין, שֶׁהֵן מְטַהֲרִין בְּזוֹחֲלִין. לְמַעְלָה מֵהֶן, מַיִם חַיִּים, שֶׁבָּהֶן טְבִילָה לַזָּבִים, וְהַזָּיָה לַמְצֹרָעִים, וּכְשֵׁרִים לְקַדֵּשׁ מֵהֶן מֵי חַטָּאת:
Above these [<i>mikvaot</i> described thus far, and next in the hierarchy of <i>mikvaot</i>,] are blighted waters, which purify even when flowing. Above these are living waters [i.e. pure, potable spring waters], that with them <i>zavim</i> [individuals who have certain types of atypical genital discharges, which render them impure] may be purified, and lepers may be sprinkled [as part of the process of purifying them], and they [these waters] are valid for use for the <i>chatat</i> ritual [i.e. to sanctify them with the ashes of a red heifer as part of the purification ritual].