Tap water in CB21, CambridgeSafe to drink.Very hard.
Supplied by Cambridge Water. 8,410 samples, 21 substances, latest on 20 December 2024. Everything is inside the legal limit. One result, nitrate, sits close to the line.
9.1 / 10
The tank is as full as the score. The specks are the minerals that make water hard.
What to do about it
Hard water: compare softener quotes
At 330 mg/L a softener is the only thing that stops limescale. Filters do not soften water.
It pays for itself in most homes at this hardness, through a boiler that stays efficient and appliances that last.
Waterdrop G3P600 Reverse Osmosis
£550typical price
Removes nitrate, the result that stood out in CB21.
Osmio PRO-III Ultimate Whole House
£499typical price
Removes nitrate, the result that stood out in CB21.
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What's in a glass of CB21 water
Every bubble is a substance the lab measured. The higher it floats, the closer it came to its legal limit, the dashed line at the top.
Nitrate came closest to a limit, at 75% of it. 18 of 19 substances used under a quarter of theirs.
- Nitrate75%
- Nickel14%
- Fluoride12%
- Colour10%
- Arsenic10%
- Lead9%
- Mercury4%
- Antimony4%
- Boron4%
- Trihalomethanes4%
- Iron4%
- Manganese3%
- Aluminium3%
- Turbidity3%
- Copper3%
- Cadmium2%
- Chromium2%
- Selenium2%
- Nitrite<1%
- Coliform Bacteria none found
- Conductivity 584 µS/cm
All 21 results as a table
| Substance | Result | Legal limit | Share of limit |
|---|---|---|---|
| Nitrate | 37.6 mg/L | 50 mg/L | 75% |
| Colour | 2 mg/L Pt/Co | 20 mg/L Pt/Co | 10% |
| Turbidity | 0.12 NTU | 4 NTU | 3% |
| Coliform Bacteria | 0 count/100ml | Must be zero | None found |
| Conductivity | 584 µS/cm | No legal limit | – |
| Trihalomethanes | 0.00397 mg/L | 0.1 mg/L | 4% |
| Nitrite | 0.004 mg/L | 0.5 mg/L | <1% |
| Aluminium | 0.0061 mg/L | 0.2 mg/L | 3% |
| Iron | 0.0073 mg/L | 0.2 mg/L | 4% |
| Manganese | 0.0017 mg/L | 0.05 mg/L | 3% |
| Copper | 0.053 mg/L | 2 mg/L | 3% |
| Fluoride | 0.178 mg/L | 1.5 mg/L | 12% |
| Arsenic | 0.001 mg/L | 0.01 mg/L | 10% |
| Cadmium | 0.00012 mg/L | 0.005 mg/L | 2% |
| Chromium | 0.001 mg/L | 0.05 mg/L | 2% |
| Mercury | 0.00004 mg/L | 0.001 mg/L | 4% |
| Nickel | 0.0029 mg/L | 0.02 mg/L | 14% |
| Lead | 0.0009 mg/L | 0.01 mg/L | 9% |
| Antimony | 0.0002 mg/L | 0.005 mg/L | 4% |
| Selenium | 0.0008 mg/L | 0.04 mg/L | 2% |
| Boron | 0.04 mg/L | 1 mg/L | 4% |
330mg of limescale minerals in every litre, typical for the CB area. CB21 has no reading of its own.
This is the water that furs up kettles
Very hard on the UK scale. It is fine to drink. It is hard on boilers, showers, skin and anything that heats water, and a jug or tap filter will not change that.
Softener quotes for CB21
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Your river is the Bottisham Lode - Quy Water, rated moderate
The Environment Agency rated the Bottisham Lode - Quy Water as moderate for ecological health in its 2025 assessment, meaning the river is noticeably changed by pollution or engineering. It is held back by phosphate and dissolved oxygen. It fails the chemical test, as every river, estuary and stretch of coast in England does, because of long-lasting pollutants such as mercury, PFOS (a forever chemical) and old flame retardants.
None of this is a test of your tap water. Environment Agency record · River health across England
69
forever-chemical detections in nearby rivers and groundwater
At 3 sites. The highest was PFBS at 0.0046 µg/L, at Sawston Inv.springfield Rd.upwelling, 8.0 km away, in September 2023. These are river and borehole samples, not tests of your tap water.
Every PFAS sample around Cambridge · Which filters remove PFAS · PFAS explained
CB21 in short
Tap water in CB21 (Cambridge) is supplied by Cambridge Water in the Cambridge Central zone and scores 9.1 out of 10, against an England and Wales average of 9.0. 1 of 21 tested substances was close to or over a limit. The latest sample is from 20 December 2024.
- Nitrate is within its legal limit but flagged, at 75% of the 50 mg/L maximumAnything over three quarters of a limit is flagged here as worth watching. It has not gone over. See every reading
- The cleanest tap water of the 6 areas tested in CambridgeCB21 scores 9.1 out of 10, ahead of CB3 in second place on 9.1. Every area in Cambridge
- Among the hardest water in the country at 330 mg/LVery hard starts at 250 mg/L. At this level kettles scale up within weeks and a softener is a normal purchase across the CB postcode area. How hardness is measured
Questions about CB21 water
Is CB21 tap water safe to drink?
Based on the latest tests, CB21 (Cambridge) water scores 9.1/10, which is safe. 1 of 21 tested contaminants exceeded recommended levels. Water is supplied by Cambridge Water.
What contaminants are in CB21 water?
We tested 21 contaminants in CB21 water. 1 were flagged, including Nitrate. PFAS (forever chemicals) were also measured in rivers and groundwater within 10 km, though not in the tap-water tests themselves.
Who supplies water in CB21?
CB21 (Cambridge) is supplied by Cambridge Water. You can view their full profile and compliance data on our supplier page.
Is CB21 water hard or soft?
No hardness reading has been published for CB21 itself. Across the CB postcode area the typical value is 330 mg/L CaCO3, which is classified as very hard. Hard water can cause limescale buildup. A water softener or filter jug may help.
Should I use a water filter in CB21?
With 1 contaminant above recommended levels in CB21, a water filter could help. A reverse osmosis or activated carbon filter is recommended for PFAS removal. See our filter recommendations for your area.
Are there PFAS forever chemicals in CB21 water?
The tap-water tests we hold for CB21 do not include a PFAS result. Environment Agency monitoring found PFAS in 69 river and groundwater samples from 3 sites within 10 km of CB21, the highest being PFBS at 0.0046 µg/L about 8 km away. These are environmental samples, not tests of tap water. The UK currently has no legal limit for PFAS in drinking water; the Drinking Water Inspectorate uses a 0.1 µg/L guideline for individual compounds. Reverse osmosis filters can reduce PFAS levels.
How clean is the river near CB21?
The Environment Agency rated the Bottisham Lode - Quy Water as moderate for ecological health in its 2025 assessment, meaning the river is noticeably changed by pollution or engineering. It is held back by phosphate and dissolved oxygen. It fails the chemical test, as every river, estuary and stretch of coast in England does, because of long-lasting pollutants such as mercury, PFOS (a forever chemical) and old flame retardants. This is a rating of the river, not of tap water in CB21, which is treated before it reaches homes.
Keep reading
- Best Filter for PFAS RemovalThe filters with independent certification to remove forever chemicals
- PFAS Forever ChemicalsWhat PFAS are and how to reduce your exposure at home
- Best Water Softener UKHarvey, Kinetico, BWT, Monarch and Water2Buy compared, with real costs
- Do I Need a Water Softener?The hardness bands, the symptoms, and a postcode check
- UK Water Hardness MapIs your water hard or soft, and does it matter?
- Best Water Filters UKEvery filter type compared on what it actually removes
- Do I need a water softener?The hardness bands, the symptoms, and when the answer is no
- Best water softener UKHarvey, Kinetico, BWT, Monarch and Water2Buy compared
- Water softener costUnit, fitting and salt, and how long the payback takes
- Installation explainedWhere it goes, the bypass tap, the drain, DIY or plumber
- Harvey vs KineticoThe two premium twin-cylinder brands, side by side
- Softener salt guideTablet, block or granular, and how much you get through
- Salt-free softenersConditioners and electronic descalers, honestly assessed
PFAS explainedNitrate levelsHow to test your waterBest water filtersFilter shower headsWater testing kitsAll of CambridgeUK water rankingsWater hardness checkerWater hardness map
River and groundwater readings near CB21
Environment Agency samples from rivers, groundwater and reservoirs nearby. Not your tap water. For scale they are shown against drinking water limits; rivers are judged against much stricter environmental standards, and on those every river in England fails for chemicals.
Get alerts for your area
We'll email you when water quality data changes for CB21.