Where our water data comes from

Water companies publish results for supply zones, reporting wards or other service areas. These are usually summaries of samples taken during a reporting period. They are not measurements at every postcode or every tap.

Postcodes and places

Our postcode checker uses a supplier-backed match when available. We do not substitute a nearby town when we cannot verify a postcode. Older town pages may show a surrounding supply area; this does not establish which zone supplies every address in that town.

Measurements and missing values

We retain the reported value, unit, period, source, available sample counts and qualifiers. “Less than 0.67” stays a less-than result; it does not become an exact 0.67 reading. Missing hardness is unavailable, not zero or soft water. We do not derive hardness from conductivity without a validated method for that source.

Dates and updates

The reporting period tells you when the measurements relate to. The retrieval date tells you when a source was collected; the source-check date tells you when it was last checked. A newly retrieved report can still contain older measurements. Report histories are being assembled, and coverage is incomplete.

Hardness and comparisons

Hardness is expressed as mg/l of calcium carbonate equivalent. Our categories are soft up to 100, slightly hard above 100 to 150, moderately hard above 150 to 200, hard above 200 to 300, and very hard above 300 mg/l. Appliance conversions use rounded household factors: divide by 100 for mmol/l, multiply by 0.056 for German degrees, 0.1 for French degrees and 0.07 for Clark degrees.

We compare historical hardness only where the reporting area, metric and units match. Changes in zone boundaries, sampling or methodology can affect comparisons. Two annual values do not establish a sustained trend.

What results can tell you

Hardness describes minerals and is not a health score. A mean below a limit does not mean every sample complied. Historical exceedances need the supplier’s investigation and context; they do not by themselves establish a current incident at your property.

Read the linked original report alongside our summary. If the source differs, tell us about a correction.