Rain percolating through chalk dissolves calcium carbonate, and that dissolved mineral is what makes water hard. The Drinking Water Inspectorate classifies hardness in bands from soft to very hard, and this region sits in the upper bands.
The geology
Rain is slightly acidic – it dissolves carbon dioxide from the air as it falls, forming a weak carbonic acid solution. When that rain lands on chalk or limestone, it slowly dissolves the calcium carbonate the rock is made of.
East Anglia sits on a substantial chalk aquifer. Water percolating down through it picks up dissolved calcium and magnesium on the way, and that dissolved mineral load travels with it to the abstraction point, through the treatment works, along the mains and out of your tap.
Treatment removes pathogens and particulates. It does not, generally, remove hardness – softening at a treatment works is possible but it is not the normal practice for a supply of this kind. So the hardness arrives at your house essentially as the geology delivered it.
The consequence is that hardness is a regional characteristic rather than a local fault. It is not something wrong with your pipes or your supply. It is the rock.
The official classification
The Drinking Water Inspectorate is the statutory regulator for drinking water in England and Wales, and it publishes the classification bands used across the industry:
| Classification | mg/l calcium carbonate |
|---|---|
| Soft | up to 100 |
| Slightly hard | 100 to 150 |
| Moderately hard | 150 to 200 |
| Hard | 200 to 300 |
| Very hard | more than 300 |
Those are the bands to use. Manufacturers sometimes publish their own scales with different boundaries, generally arranged so that more customers fall into a band that suits the product being sold.
You will find websites quoting a specific hardness figure for Norwich or for Norfolk. Those figures are third-party aggregations whose provenance we have not been able to verify against the water company, and we are not prepared to publish a number we cannot stand behind. Anglian Water publishes the figure for your supply zone on its own water quality portal, and that is the authoritative source. The DWI itself notes that there is local variation not captured by regional maps and recommends asking your supplier directly.
The units, because you will meet several
Hardness gets reported in several units and customers arrive holding whichever one their appliance manual used. They all describe the same thing:
| Unit | Convert from mg/l CaCO3 by |
|---|---|
| Degrees Clark (Clark, English) | divide by 14.254 |
| French degrees (fH) | divide by 10 |
| German degrees (dH) | divide by 17.848 |
| Parts per million (ppm) | the same number – ppm and mg/l are equivalent here |
| Grains per gallon (imperial) | 1 grain per imperial gallon = 1 degree Clark = 14.254 mg/l |
Softener manufacturers in particular specify in different units depending on where the machine was designed, which is why a machine set up from the wrong unit can be badly misconfigured. Our water hardness checker shows the bands and does the conversions.
What hardness actually does
Dissolved calcium stays dissolved in cold water. It comes out of solution when the water is heated, and it deposits on the hottest surface available – which is always a heat transfer surface, because that is where the heat is.
- Boiler heat exchangers, where scale insulates the surface whose entire purpose is to transfer heat.
- Combi plate heat exchangers, where scale both insulates and restricts flow – which is why hot water pressure on a combi declines over the years in this county.
- Hot water cylinder coils, so the cylinder heats slowly and never quite gets there.
- Immersion heater elements, which scale, overheat inside their own deposit, and burn out.
- Shower heads and tap aerators, which block progressively.
- Tap cartridges, where abrasive scale particles score the ceramic discs so taps drip and stiffen far sooner than they should.
- Washing machines, dishwashers and coffee machines, all of which heat water.
- Pipework bore, very slowly, over decades.
The pattern worth noticing: hardness does not damage plumbing generally. It damages specifically the things that heat water, which are the expensive things. See what limescale actually does.
The things people think are faults
- Scum on tea and in the bath. Calcium reacting with soap to form an insoluble residue. Not dirt, not a fault, and it disappears entirely with softened water.
- Soap that will not lather. The calcium is consuming the soap before it can do its job, which is why detergent use is measurably higher in hard water areas.
- Cloudy glassware from the dishwasher, which is scale deposited as the water evaporates.
- White deposits round taps and on shower screens. The visible tip of the iceberg, and the least important part of it.
- Dry skin and hair, which many people notice changing when they move between hard and soft water areas.
- A kettle that furs. The clearest demonstration of the mechanism – you can watch it happen.
None of these are faults with your plumbing. They are what hard water does, and the only way to change them is to change the water.
What to do about it
Three genuinely different options, and they solve different problems:
| Option | What it does | Right when |
|---|---|---|
| Do nothing | Accept scale as a maintenance cost | Low hot water demand, and you do not mind descaling things |
| Scale inhibitor | Prevents scale adhering to heat exchange surfaces downstream | Protecting a boiler is the priority, space is limited, and there is no drain |
| Water softener | Removes hardness entirely – no scale anywhere, and soap behaves differently | There is a cylinder to protect, a whole house to treat, and space for a unit |
The distinction that matters: an inhibitor protects equipment, a softener changes the water. See softener or scale inhibitor.
Wondering whether it is worth treating? The question is mostly whether you have a cylinder and how much hot water the house uses.
Questions we get asked about this
How hard is the water in Norfolk?
Regionally it sits in the upper classification bands. We do not publish a specific figure because we have not been able to verify the numbers circulating online against the water company. Anglian Water publishes the figure for your supply zone on its own portal, and that is the source to use.
Is hard water bad for you?
No. Dissolved calcium and magnesium are not harmful and some research has associated hard water areas with modest health benefits. The problem hard water causes is to equipment, not to people.
Why does my kettle fur up so quickly?
Because the element is the hottest surface in the kettle and that is where dissolved calcium comes out of solution. It is the same process happening invisibly inside your boiler and cylinder.
Does the water company soften the water?
Treatment removes pathogens and particulates. Softening at a treatment works is technically possible but is not the normal practice for a supply of this kind, so the hardness arrives essentially as the geology delivered it.
Will a filter jug soften my water?
A domestic filter jug improves taste and reduces some hardness in the water passing through it, but it treats a jug at a time. It does nothing for the water reaching your boiler, cylinder or washing machine, which is where the actual cost is.
Is it worth moving to soft water?
If you have a cylinder and a reasonable hot water demand, the equipment protection argument is strong. If you have a small flat and a combi used lightly, an inhibitor may be proportionate. It is worth being honest about which you are.
Sources
- Drinking Water Inspectorate, water hardness classification and guidance — https://www.dwi.gov.uk/consumers/learn-more-about-your-water/water-hardness-hard-water/
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