Pipes & Heat in Old Cambridge

A reading site on water and heating in older Cambridge and South Cambridgeshire homes. Not a plumbing or heating firm.

Inside this site

Hard water ยท In brief

Finding the hardness figure for your own address

For water hardness by postcode, ask the water company named on your bill for your current figure. National maps and websites give only the broad picture, and DWI says not to buy from door-to-door testers.

Most useful for: Cambridge and South Cambs householders, tenants and buyers choosing a softener or boiler

Compiled from the sources at the end. Updated .

Long straight terraced street of painted and pale brick houses under blue sky, cars parked along one side.
A long terraced street with pale brick and painted house fronts.

The Drinking Water Inspectorate (DWI) warns of local variation not shown on its map and tells readers to ask their water company. Around Cambridge, that first means working out which company it is: Cambridge Water or Anglian Water, and your bill will say.

Getting and reading the figure

  1. Ask the company for the current hardness at your postcode, and when it was sampled.
  2. Check the units. DWI's bands use mg/l as calcium carbonate, and mg/L is the same as ppm.
  3. Compare it with the bands on the hardness page. Very hard starts over 300.
  4. Note whether it is over 200 ppm, the line Approved Document L uses for hard water, and give it to your boiler installer.

Postcode websites can help as a rough cross-check. TapWater.uk, a secondary source that sells softener quotes, shows 330 mg/L for CB1, but says no reading is published for that district and that this is the area's typical value. So a figure there is not a measurement at your house.

Testers and test kits

DWI says not to buy from door-to-door sellers offering water tests, and to report them to trading standards. A free doorstep test is not a reason to buy anything.

A home kit gives you a reading from your own tap on one day. Check which units it reports in before comparing with the bands above, since American kits may not use mg/L. It will not tell you anything about lead: for that, the company tests at the kitchen tap on request.

Sources, read 4 November 2026: Drinking Water Inspectorate: water hardness; Drinking Water Inspectorate: filters and softeners; Drinking Water Inspectorate: standards and regulations; Approved Document L, Volume 1 (2021 with 2023 amendments); TapWater.uk: CB1 (secondary, sells softener quotes).