DannyD. wrote, on Tue, 01 Jul 2014 03:29:41 +0000:

I don't think the law *requires* the cistern, but, the tank farm
I just visited had five 5,000 gallon tanks, plus what I call a
~20,000 gallon "cistern" and another 500 gallon water tank.

I think I got the *direction* of flow wrong in that
description. I'll have to re-annotate.