Hardest Water Areas UK: 50 Worst Postcodes Ranked (2026)

#	Postcode	Town	Water Company	Hardness	PPM
1	CM19	Harlow	Anglian Water	394	394 ppm
2	CM18	Harlow	Anglian Water	393	393 ppm
3	IP33	Bury St Edmunds	Anglian Water	393	393 ppm
4	CM17	Harlow	Anglian Water	392	392 ppm
5	IP32	Bury St Edmunds	Anglian Water	392	392 ppm
6	NR19	Dereham	Anglian Water	392	392 ppm
7	CM16	Epping	Anglian Water	391	391 ppm
8	IP31	Bury St Edmunds	Anglian Water	391	391 ppm
9	NR18	Wymondham	Anglian Water	391	391 ppm
10	CM15	Brentwood	Anglian Water	390	390 ppm
11	IP30	Bury St Edmunds	Anglian Water	390	390 ppm
12	NR17	Attleborough	Anglian Water	390	390 ppm
13	CM14	Brentwood	Anglian Water	389	389 ppm
14	NR16	Norwich	Anglian Water	389	389 ppm
15	CM13	Brentwood	Anglian Water	388	388 ppm
16	NR15	Norwich	Anglian Water	388	388 ppm
17	CM12	Billericay	Anglian Water	387	387 ppm
18	NR14	Norwich	Anglian Water	387	387 ppm
19	CM11	Billericay	Anglian Water	386	386 ppm
20	NR13	Norwich	Anglian Water	386	386 ppm
21	LN9	Horncastle	Anglian Water	385	385 ppm
22	NR12	Norwich	Anglian Water	385	385 ppm
23	LN8	Market Rasen	Anglian Water	384	384 ppm
24	NR11	Norwich	Anglian Water	384	384 ppm
25	LN7	Market Rasen	Anglian Water	383	383 ppm
26	NR10	Norwich	Anglian Water	383	383 ppm
27	LN6	Lincoln	Anglian Water	382	382 ppm
28	LN5	Lincoln	Anglian Water	381	381 ppm
29	LN4	Lincoln	Anglian Water	380	380 ppm
30	LN3	Lincoln	Anglian Water	379	379 ppm
31	LN2	Lincoln	Anglian Water	378	378 ppm
32	SG9	Buntingford	Anglian Water	378	378 ppm
33	LN1	Lincoln	Anglian Water	377	377 ppm
34	SG8	Royston	Anglian Water	377	377 ppm
35	SG7	Baldock	Anglian Water	376	376 ppm
36	SG6	Letchworth Garden City	Anglian Water	375	375 ppm
37	SG5	Hitchin	Anglian Water	374	374 ppm
38	CB25	Cambridge	Anglian Water	373	373 ppm
39	SG4	Hitchin	Anglian Water	373	373 ppm
40	CB24	Cambridge	Anglian Water	372	372 ppm
41	SG3	Knebworth	Anglian Water	372	372 ppm
42	CB23	Cambridge	Anglian Water	371	371 ppm
43	SG2	Stevenage	Anglian Water	371	371 ppm
44	CB22	Cambridge	Anglian Water	370	370 ppm
45	SG1	Stevenage	Anglian Water	370	370 ppm
46	CB21	Cambridge	Anglian Water	369	369 ppm
47	PE9	Stamford	Anglian Water	367	367 ppm
48	CM9	Maldon	Anglian Water	366	366 ppm
49	IP29	Bury St Edmunds	Anglian Water	366	366 ppm
50	PE8	Peterborough	Anglian Water	366	366 ppm

Where Is Water Hardest in the UK?

The hardest water in the UK is found in the South East, East Anglia, and parts of the East Midlands. These areas sit on chalk and limestone bedrock that dissolves calcium carbonate into the water supply as groundwater percolates through it. Some postcodes in Cambridgeshire and Hertfordshire regularly exceed 400 ppm — more than six times the level found in Scottish water.

Hard Water Regions at a Glance

South East England: Thames Water, South East Water, and Southern Water all draw from chalk aquifers beneath the North and South Downs. Typical readings: 250–380 ppm. London averages around 280 ppm, with some boroughs exceeding 340 ppm.

East Anglia: Anglian Water serves some of the hardest water in Europe. Borehole-sourced postcodes in Norfolk, Suffolk, and Cambridgeshire routinely hit 350–420 ppm. Surface-water areas (Rutland Water, Grafham Water) are slightly lower at 200–280 ppm.

East Midlands: Parts of Lincolnshire and Northamptonshire served by Anglian Water see readings above 300 ppm, driven by the same limestone belt that extends from the Cotswolds to the Humber.

Yorkshire (East): Yorkshire Water supplies vary widely. Western moorland sources (Leeds, Bradford) are moderately soft (60–120 ppm), but the chalk Wolds in the East Riding push readings above 300 ppm in Hull and Bridlington.

What Hard Water Does to Your Home

Water above 200 ppm causes visible limescale build-up within weeks. The practical effects are cumulative:

Boiler efficiency drops — the British Water Treatment Association estimates 1.6 mm of limescale increases energy use by 12%. In very hard water areas, this adds £150–200/year to bills.
Appliance lifespan shortens — kettles, washing machines, and dishwashers in hard water areas last 2–3 years less than in soft water areas.
Skin and hair issues — a 2018 King's College London study linked hard water to increased eczema severity. Read our hard water and skin guide.
Higher product use — soap, shampoo, and detergent don't lather as well in hard water, so households use 30–50% more product.

How to Fix Hard Water

The most effective solution is a whole-house water softener (£400–£1,500 installed). For a lower-cost approach, a shower filter (£20–30) protects skin and hair, while a boiler scale inhibitor (£60–120) prevents the most expensive limescale damage. See all solutions compared.

Frequently Asked Questions

Which UK water company has the hardest water?

Anglian Water and Affinity Water consistently report the highest average hardness, both above 300 ppm. Thames Water is close behind at 260–290 ppm average.

Is hard water dangerous to drink?

No. Hard water is safe and provides dietary calcium and magnesium. The World Health Organisation confirms no adverse health effects from drinking hard water. The problems are domestic — limescale, appliance damage, and skin irritation — not health risks.

Can I check my exact water hardness?

Yes — enter your postcode at WaterHard.uk for an instant reading. For a precise measurement, use a home water hardness test (strip tests from £5, digital meters from £20).

Compare these results with the 50 softest water areas in the UK to see the full range.

Hardest Water Areas in the UK