Over 60% of homes in the UK suffer from hard or aggressively hard tap water. If you live in London, East Anglia, or the South East, dissolved calcium carbonate ($CaCO_3$) wrecks kettle elements, scales combi boiler heat exchangers, and clouds glassware.

Most homeowners only find out their water hardness when a new appliance (like a Bosch or Miele dishwasher) asks for manual hardness calibration (H:00 to H:07) or salt dosage settings.

To solve this, I built WaterHardness.uk — an independent data platform and utility engine mapping water hardness metrics across 9,000+ UK postcode sectors.

Here is a breakdown of the technical challenges, data normalization, and appliance calibration logic behind the project.

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