Midrasch zu Sukkah 3:3

Rabbi Phineas said: In the future the waters of the well will ascend from under the threshold of the Temple, and they will overflow and bubble over and issue forth and become twelve streams corresponding to the twelve tribes, as it is said, "And he brought me back unto the door of the house; and behold, waters issued out from under the threshold of the house eastward, for the forefront of the house was toward the east: and the waters came down from under, from the right side of the house, on the south of the altar" (Ezek. 47:1). Three (streams) towards the south to pass through them up to the ankles, and three (streams) towards the west to pass through them up to the knees, as it is said, "When the man went forth eastward with the line in his hand, he measured a thousand cubits, and he caused me to pass through the waters, waters that were to the ankles. Again he measured a thousand, and he caused me to pass through the waters, waters that were to the knees" (Ezek. 47:3, 4). And three (streams) towards the east to pass through them up to the neck, for the neck is the extremity of the body, as it is said, "And he measured a thousand cubits, and he caused me to pass through the waters that were to the extremity" (Ezek. 47:3). And (the waters) descended to the brook of Kidron, and they rose higher than in "the stream, that I could not pass through" (Ezek. 47:5), as it is said, "For the waters were risen, waters to swim in, a stream that could not be passed through" (ibid.). And the waters are drawn (thence), and they flow down to the fords of the Jordan, as it is said, "And they shall go down into || the Arabah" (Ezek. 47:8).