thanks for this info. I was just checking out a 600 gallon cistern for about $900, but it was above ground.

It seems that the main appeal to an underground cistern is an improved ability to catch runoff and stay dark (anti-algae). Being underground doesn't give you the land back because you don't want to be doing anything on top of it (for safety's sake)

The above ground cistern has the appeal that you can't fall in it (ok, "as easily") and you can drain it from the bottom... the whole gravity feed, head pressure situation. And rainwater is generally safe to use (although rainwater running off your coal tar roof would not be).

Still, I'm not sure if the above or below is clearly better.

Is there any other benefit I'm missing?