הלכה על פרה 6:10

From the laws of the commandment - that which they said (Mishnah Parah 6:5) that we only fill the waters that we put on the ashes, with a vessel, from the bubbling springs and from the flowing rivers; [that] the placing of the waters on the ashes is called by our Rabbis, may their memory be blessed, the "sanctification of the sin-offering waters"; [that] the waters that he places upon the ashes are called the "niddah waters" by the verse; [that] all are fit to fill the waters and to sanctify, except for a deaf-mute, a mentally incapacitated person or a minor (Mishnah Parah 10:4); [that] one who is involved in another work at the time of filling the waters or in bringing them, disqualifies them (Mishnah Parah 4:4), but that after he puts the ashes in them, [other] work does not disqualify them; [that] a wage also disqualifies in the sanctification and the sprinkling (Bekhorot 29a), [such that] the waters and ashes of one who takes a wage to sanctify or sprinkle are like the [regular] waters of a cave and like the [regular] ashes of an oven, but one who takes a wage for the filling [of the waters] does not disqualify [them]; and the rest of its many details - are [all] elucidated in Tractate Parah (see Mishneh Torah, Laws of Red Heifer 1).