In Maryland, mains water is delivered by local public water systems, regulated by the Maryland Dept of the Environment (MDE), Water & Science Administration under the US EPA Safe Drinking Water Act. Typical hardness: Variable; softer on the Eastern Shore / coastal plain, moderately hard to hard in the Piedmont and western limestone areas. For a specific ZIP, see the EWG Tap Water Database.
Sources: Maryland Dept of the Environment (MDE), Water & Science Administration, EWG Tap Water Database