Fountain and Stream

The second image Athanasius uses to defend the eternality of the Son is that of the fountain and the stream:
  "Just as a fountain is no fountain without a stream flowing from it, so the Father is no Father without a Son." - Leithart, Athanasius, p47.
Jeremiah calls Yahweh the "fountain of living waters" (Jer 3:12) and thus the basis for Athanasius' second image.