Tap water in CM23, East HertfordshireSafe to drink.Very hard.
Supplied by Affinity Water. 923 samples, 24 substances, latest on 16 December 2025. Everything is inside the legal limit. One result, nitrite, sits close to the line.
9.0 / 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 345 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
Maximum contaminant removal including PFAS and fluoride
Waterdrop 10UA Under Sink
£70typical price
High-volume under-sink filtration without RO complexity
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What's in a glass of CM23 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.
Nitrite came closest to a limit, at 94% of it. 19 of 21 substances used under a quarter of theirs.
- Nitrite94%
- Nitrate47%
- Fluoride15%
- Bromate15%
- Ammonia12%
- Colour10%
- Lead7%
- Boron5%
- Iron4%
- Nickel4%
- Trihalomethanes3%
- Selenium3%
- Arsenic3%
- Turbidity3%
- Mercury2%
- Antimony1%
- Cadmium1%
- Aluminium<1%
- Chromium<1%
- Manganese<1%
- Copper<1%
- E. coli none found
- Coliform Bacteria none found
- Conductivity 642 µS/cm
All 24 results as a table
| Substance | Result | Legal limit | Share of limit |
|---|---|---|---|
| Nitrite | 0.47 mg/L | 0.5 mg/L | 94% |
| E. coli | 0 count/100ml | Must be zero | None found |
| Mercury | 0.000023 mg/L | 0.001 mg/L | 2% |
| Boron | 0.046 mg/L | 1 mg/L | 5% |
| Coliform Bacteria | 0 count/100ml | Must be zero | None found |
| Colour | 2 mg/L Pt/Co | 20 mg/L Pt/Co | 10% |
| Cadmium | 0.000054 mg/L | 0.005 mg/L | 1% |
| Turbidity | 0.1 NTU | 4 NTU | 3% |
| Manganese | 0.000363 mg/L | 0.05 mg/L | <1% |
| Fluoride | 0.221 mg/L | 1.5 mg/L | 15% |
| Ammonia | 0.06 mg/L | 0.5 mg/L | 12% |
| Conductivity | 642 µS/cm | No legal limit | – |
| Chromium | 0.000383 mg/L | 0.05 mg/L | <1% |
| Aluminium | 0.00199 mg/L | 0.2 mg/L | <1% |
| Antimony | 0.000058 mg/L | 0.005 mg/L | 1% |
| Iron | 0.00897 mg/L | 0.2 mg/L | 4% |
| Arsenic | 0.00026 mg/L | 0.01 mg/L | 3% |
| Bromate | 0.00147 mg/L | 0.01 mg/L | 15% |
| Lead | 0.000673 mg/L | 0.01 mg/L | 7% |
| Nickel | 0.000886 mg/L | 0.02 mg/L | 4% |
| Trihalomethanes | 0.00347 mg/L | 0.1 mg/L | 3% |
| Selenium | 0.00117 mg/L | 0.04 mg/L | 3% |
| Nitrate | 23.5 mg/L | 50 mg/L | 47% |
| Copper | 0.007 mg/L | 2 mg/L | <1% |
345mg of limescale minerals in every litre
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 CM23
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Your river is the Stort and Navigation, B Stortford to Harlow, rated moderate
The Environment Agency rated the Stort and Navigation, B Stortford to Harlow as moderate for ecological health in its 2025 assessment, meaning the river is noticeably changed by pollution or engineering. It is held back by fish and phosphate. 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
CM23 in short
Tap water in CM23 (East Hertfordshire) is supplied by Affinity Water in the East Hertfordshire Central zone and scores 9.0 out of 10, against an England and Wales average of 9.0. 1 of 24 tested substances was close to or over a limit. The latest sample is from 16 December 2025.
- Nitrite is within its legal limit but flagged, at 94% of the 0.5 mg/L maximumAnything over three quarters of a limit is flagged here as worth watching. It has not gone over. See every reading
- Among the hardest water in the country at 345 mg/LVery hard starts at 250 mg/L. At this level kettles scale up within weeks and a softener is a normal purchase in CM23. How hardness is measured
- 7th cleanest of 8 areas tested in East Hertfordshire1 area in East Hertfordshire scored lower. The best is CM21 on 9.4.
Questions about CM23 water
Is CM23 tap water safe to drink?
Based on the latest tests, CM23 (East Hertfordshire) water scores 9/10, which is safe. 1 of 24 tested contaminants exceeded recommended levels. Water is supplied by Affinity Water.
What contaminants are in CM23 water?
We tested 24 contaminants in CM23 water. 1 were flagged, including Nitrite.
Who supplies water in CM23?
CM23 (East Hertfordshire) is supplied by Affinity Water. You can view their full profile and compliance data on our supplier page.
Is CM23 water hard or soft?
Water in CM23 (East Hertfordshire) has a hardness of 345 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 CM23?
With 1 contaminant above recommended levels in CM23, a water filter could help. A filter jug or under-sink filter can reduce most common contaminants. See our filter recommendations for your area.
Are there PFAS forever chemicals in CM23 water?
No PFAS (forever chemicals) result is attached to the tap-water tests for CM23, and the Environment Agency has no PFAS detections in rivers or groundwater within 10 km of it. That reflects where sampling has happened as much as the water itself.
How clean is the river near CM23?
The Environment Agency rated the Stort and Navigation, B Stortford to Harlow as moderate for ecological health in its 2025 assessment, meaning the river is noticeably changed by pollution or engineering. It is held back by fish and phosphate. 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 CM23, which is treated before it reaches homes.
Keep reading
- 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
Nitrate levelsHow to test your waterBest water filtersFilter shower headsWater testing kitsUK water rankingsWater hardness checkerWater hardness map
River and groundwater readings near CM23
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 CM23.