Mains water in Hertfordshire (England) is supplied by Affinity Water (most); Thames Water (south); Anglian Water (small NE); typical hardness: Very hard, ~303 mg/l CaCO3 (range 239 to 378). Water quality is regulated by the Environment Agency · Ofwat · Drinking Water Inspectorate.
Sources: Affinity Water (most); Thames Water (south); Anglian Water (small NE)