וְלָֽקְחוּ֙ לַטָּמֵ֔א מֵעֲפַ֖ר שְׂרֵפַ֣ת הַֽחַטָּ֑את וְנָתַ֥ן עָלָ֛יו מַ֥יִם חַיִּ֖ים אֶל־כֶּֽלִי׃
And for the unclean they shall take of the ashes of the burning of the purification from sin, and running water shall be put thereto in a vessel.
Read kabbalistic (mystical) interpretation of Numbers 19:17: and classical mystical sources.