The argument centers around whether Springhill's normal policies currently discourage water conservation. How emergency measures are enforced isn't relevant to that.

We have no idea how high the threshold was to begin with. If it's not extremely high already, refusing to raise the threshold suggests a concern with conserving water, which potentially even weakens the author’s argument.

Most households never hit the threshold, which means they never pay the per-liter fee. This strengthens the argument by showing that Springhill indeed isn’t encouraging people to cut back on their water usage.

This doesn’t give us enough information, because we don't know anything about the neighboring towns. The threshold may still be high enough that most people never pay the per-liter fee—we can't say.

This simply tells us how the threshold is set. We need to know if it’s set high enough that most households never pay the per-liter rate. Since this doesn't tell us, it's irrelevant.