It may also be worth noting that "apsu" or "absu" is the Babylonian word for
well (as in the above mentioned
fresh water).
Wells and
springs are often symbolic of deep and
hidden knowledge, such as that which might be found with those that are older than the
gods (see
Prometheus and the other
Greek Titans).
The soft link below to the word abyss makes me think it might be quite possible that this, too, is etymologically related. Just a speculation.