Mayim chayim. Living water. The Hebrew is plural: living waters. In the Tanakh, the phrase names water that flows or has flowed, fed by spring, river, sea, or rain. Halakhah requires it for a valid mikvah. Stagnant water alone does not qualify. The water has to have touched the natural world, the world HaShem made, before it touches the body.

KJV, ESV, NASB, and NIV translate mayim chayim as "living water," which is correct word-for-word and yet misses the texture. English readers hear "living water" as a metaphor: Yeshua's offer to the Samaritan woman at the well, the river of life in Revelation, the eschatological promise. All of that is real. None of it is the whole. Mayim chayim in the Tanakh is also concrete. It is the spring at Gihon, the Jordan, the rain that fills the cistern. It is the substrate Yeshua draws on when he tells the woman at the well that whoever drinks of the water he gives will never thirst.

Living water is alive because it has been somewhere. The mikvah counts because the water counts. The water counts because HaShem made it move.