My water supply
Water hardness
When water falls as rain, it's "soft" and free of minerals.
It picks up naturally occurring minerals, such as calcium and magnesium, as it passes through rock, sand and soil. This causes the water to become ‘hard.’
All the water we supply is ‘hard’ together with more than 60% of homes in the UK.
The picture shows a comparison with other areas in the UK.
Hard water in your home
Find out more about hard water in your home
Find out how hard the water is in your home
1. Find the water quality zone for your area
2. Use the water quality zone to read the table below:
| Zone | Zone Name | Alkalinty (Average mg/l) | Calcium (Average mg/l) |
Calcium CACO3 (Average mg/l) |
Magnesium (Average mg/l) | Magnesium CaCO3 (Average mg/l) | Total Hardness mg/l or ppm CaCO3 |
Degrees Clark | Degrees French | Degrees German |
| Z1 | Cambridge North | 293 | 112 | 280 | 4.16 | 17.1 | 297 | 20.8 | 29.7 | 16.7 |
| Z2 | Cambridge South | 305 | 120 | 300 | 4.66 | 16.4 | 316 | 22.1 | 31.6 | 17.8 |
| Z4 | Linton | 337 | 117 | 293 | 5.6 | 23 | 318 | 22.3 | 31.8 | 17.9 |
| Z5 | Heydon | 288 | 100 | 250 | 3.95 | 16.3 | 266 | 18.6 | 26.6 | 14.9 |
| Z6 | Coton | 297 | 108 | 270 | 4.3 | 17.7 | 294 | 20.6 | 29.4 | 16.5 |
| Z7 | Sawston | 299 | 110 | 275 | 7.26 | 29.9 | 306 | 21.4 | 30.6 | 17.2 |
| Z8 | Odsey | 330 | 98.5 | 246 | 3.4 | 14 | 260 | 18.2 | 26 | 14.6 |
| Z10 | Earith Bridge | 274 | 115 | 287 | 2.4 | 9.9 | 297 | 20.8 | 29.7 | 16.7 |