DannyD. wrote, on Wed, 09 Jul 2014 03:09:17 +0000:

It's surprisingly hard to find how *old* the water is that we drink.

This Wikipedia on groundwater says the water "residence time" can vary
from "days to millennia" in age:
http://en.wikipedia.org/wiki/Groundwater

Here's a picture which shows it commonly is centuries to millenia
depending on the depth of the well:
http://upload.wikimedia.org/wikipedi...water_flow.svg

We know SJWC has "deep wells" because they mention them in all their
planning documents; but we don't know how deep is deep.

For my residential neighbors, anything deeper than about 500 or
600 feet would probably be considered deep (mine, at 400 feet are
constantly shutting off for lack of water, for example).