Mishnah Mikvaos 1:7: Above these [mikvaot described thus far, and next in the hierarchy of mikvaot,] is a mikveh containing forty se'ah [of water], in which one can immerse one's self and immerse other item [for purification]. Above these [mikvaot, and next in the hierarchy of mikvaot,] is a natural spring whose waters are few, and are exceeded by a greater quantity of drawn waters [which were added]. This [type of spring] is equivalent to a mikveh in that it purifies [only] when it is contained [in one place, standing still and not flowing], but [it is equivalent] to a spring in that one can immerse something in it [to purity it] when there is any amount of water [i.e. there is no minimum measure required].

לְמַעְלָה מֵהֶן, מִקְוֶה שֶׁיֶּשׁ בּוֹ אַרְבָּעִים סְאָה, שֶׁבּוֹ טוֹבְלִין וּמַטְבִּילִין. לְמַעְלָה מֵהֶן, מַעְיָן שֶׁמֵּימָיו מֻעָטִין וְרַבּוּ עָלָיו מַיִם שְׁאוּבִין, שָׁוֶה לַמִּקְוֶה לְטַהֵר בְּאַשְׁבֹּרֶן, וְלַמַּעְיָן לְהַטְבִּיל בּוֹ בְּכָל שֶׁהוּא:

Mishnah Mikvaos 1:8: Above these [mikvaot described thus far, and next in the hierarchy of mikvaot,] are blighted waters, which purify even when flowing. Above these are living waters [i.e. pure, potable spring waters], that with them zavim [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 chatat ritual [i.e. to sanctify them with the ashes of a red heifer as part of the purification ritual].

לְמַעְלָה מֵהֶן, מַיִם מֻכִּין, שֶׁהֵן מְטַהֲרִין בְּזוֹחֲלִין. לְמַעְלָה מֵהֶן, מַיִם חַיִּים, שֶׁבָּהֶן טְבִילָה לַזָּבִים, וְהַזָּיָה לַמְצֹרָעִים, וּכְשֵׁרִים לְקַדֵּשׁ מֵהֶן מֵי חַטָּאת: