Living water

Q: The B’rit Hadashah uses the imagery “living water” a lot, and I never understood what it meant.  In my Bible, Numbers 19:17 uses the words “running water” but a footnote says “living water”.  Is this where that imagery comes from?

A: Any student of the B’rit Hadashah will soon note that there is very little imagery that hasn’t been used already in the Tanakh. The imagery of the living water is no different, and you are astute to pick that out.
I am not sure which translation you are using, but they are right on! Numbers 19:17 reads in the Hebrew (transliterated), “v’lak-chu la-ta-mei may-afar s’ra-faht ha-cha-taht v’natan alav mayim chayim el-keli.” (The bolding is mine.) And the bold words literally mean, “living water,” though most translations do interpret that as running, fresh or flowing water. Now, in Jewish tradition, living water must be fresh or flowing water, as in the context of the mikveh, or ritual immersion. A mikveh isn’t considered kosher unless the water within is “living water,” that is naturally replenished, as in rain water, or flowing, like a river. So the Jewish concept of living water is tied intricately to the idea of running or flowing water.
However, the clearest imagery in the Tanakh of the living waters comes from Jeremiah. Jeremiah 2:13 reads, “For My people have committed two evils: They have forsaken Me, the fountain of living waters, And hewn themselves cisterns–broken cisterns that can hold no water.” Here, the Lord refers to Himself as the fountain of living waters. This is as compared to broken cisterns, which obviously cannot hold water. Here again is the concept of a continuous flow of water. While we, who are the broken cisterns that can’t hold water, can do nothing on our own without still being empty, if we let the living water fill us, we will continuously be filled, so that no matter how much we pour out, we will still be full. This is the origin of the imagery that John uses in chapter 4 and then again in chapter 7.