[jefftk]

You could charge tiered rates where the quantities we're talking about are incredibly expensive, enough to discourage use, without affecting what households that use far less pay.

(Or, you could, if this was legal under California law)

[sgc]

That would always wind up bankrupting at least some poor soul caught unawares. I would only support that if there were clear warnings delivered to the specific user in question beforehand (not a blanket notice to everyone that they might, but to one person indicating that they will be charged if they don't change, because they have already gone into a draconian penalty tier), in a way that you were absolutely certain the person had received notice.