Huh?
They were always frugal, because despite finding oil and getting money for
their land, they never changed. Part of the joke was they never seemed to
realize they were rich.
So they used the "cement pond" for things other than swimming. Indeed,
Granny tended to do her laundry out there, maybe even some cooking. They
kept their old truck, they kept their old clothes, they lived the same
way. I seem to recall Jed going out hunting in the Hollywood Hills.
But they probably weren't frugal, since they had no sense of being rich.
They acted like they had no money.
Michael