If I were you I would call the water department back and speak with someone who has the experience to answer your questions.
I don't live in Calumet Grove, but I always understood that the homes north of 466 have one source of water - potable water - for both in-house use and lawn sprinklers. In other words, non-potable water for the toilets doesn't make any sense.
Does you water bill show both potable and non-potable? Mine does.
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