Tap water in CM18, HarlowSafe to drink.Very hard.
Supplied by Affinity Water. 709 samples, 24 substances, latest on 15 December 2025. Everything is inside the legal limit, and nothing comes close to it.
9.3 / 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 317 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.
ZeroWater 12-Cup Ready-Pour
£40typical price
Households concerned about PFAS and heavy metals
Waterdrop 10UA Under Sink
£70typical price
High-volume under-sink filtration without RO complexity
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What's in a glass of CM18 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 47% of it. 20 of 21 substances used under a quarter of theirs.
- Nitrate47%
- Fluoride19%
- Bromate15%
- Trihalomethanes13%
- Nickel13%
- Ammonia12%
- Colour10%
- Iron7%
- Lead7%
- Boron6%
- Antimony5%
- Arsenic4%
- Turbidity3%
- Mercury2%
- Nitrite2%
- Selenium1%
- Manganese1%
- Copper1%
- Cadmium1%
- Aluminium<1%
- Chromium<1%
- E. coli none found
- Coliform Bacteria none found
- Conductivity 769 µS/cm
All 24 results as a table
| Substance | Result | Legal limit | Share of limit |
|---|---|---|---|
| Ammonia | 0.06 mg/L | 0.5 mg/L | 12% |
| E. coli | 0 count/100ml | Must be zero | None found |
| Aluminium | 0.00199 mg/L | 0.2 mg/L | <1% |
| Nitrate | 23.4 mg/L | 50 mg/L | 47% |
| Antimony | 0.000237 mg/L | 0.005 mg/L | 5% |
| Coliform Bacteria | 0 count/100ml | Must be zero | None found |
| Nitrite | 0.01 mg/L | 0.5 mg/L | 2% |
| Nickel | 0.00262 mg/L | 0.02 mg/L | 13% |
| Conductivity | 769 µS/cm | No legal limit | – |
| Manganese | 0.000646 mg/L | 0.05 mg/L | 1% |
| Iron | 0.0146 mg/L | 0.2 mg/L | 7% |
| Colour | 2 mg/L Pt/Co | 20 mg/L Pt/Co | 10% |
| Turbidity | 0.1 NTU | 4 NTU | 3% |
| Copper | 0.022 mg/L | 2 mg/L | 1% |
| Bromate | 0.0015 mg/L | 0.01 mg/L | 15% |
| Boron | 0.061 mg/L | 1 mg/L | 6% |
| Mercury | 0.000023 mg/L | 0.001 mg/L | 2% |
| Trihalomethanes | 0.0133 mg/L | 0.1 mg/L | 13% |
| Selenium | 0.000588 mg/L | 0.04 mg/L | 1% |
| Fluoride | 0.288 mg/L | 1.5 mg/L | 19% |
| Arsenic | 0.000361 mg/L | 0.01 mg/L | 4% |
| Lead | 0.000673 mg/L | 0.01 mg/L | 7% |
| Chromium | 0.000383 mg/L | 0.05 mg/L | <1% |
| Cadmium | 0.000054 mg/L | 0.005 mg/L | 1% |
317mg 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 CM18
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Your river is the Cannons Brook, rated bad
The Environment Agency rated the Cannons Brook as bad for ecological health in its 2025 assessment, meaning the river is severely damaged, with most of the expected wildlife missing. It is held back by insects and other small river life, water plants and algae 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. Its ecological rating has dropped since the previous assessment.
None of this is a test of your tap water. Environment Agency record · River health across England
CM18 in short
Tap water in CM18 (Harlow) is supplied by Affinity Water in the Harlow Central zone and scores 9.3 out of 10, against an England and Wales average of 9.0. None of the 24 tested substances came close to a limit. The latest sample is from 15 December 2025.
- The cleanest tap water of the 4 areas tested in HarlowCM18 scores 9.3 out of 10, ahead of CM19 in second place on 9.2.
- Among the hardest water in the country at 317 mg/LVery hard starts at 250 mg/L. At this level kettles scale up within weeks and a softener is a normal purchase in CM18. How hardness is measured
- Scores higher than all 3 neighbouring districtsThe nearest rival is CM19 on 9.2, against 9.3 here. Compare with CM19
Questions about CM18 water
Is CM18 tap water safe to drink?
Based on the latest tests, CM18 (Harlow) water scores 9.3/10, which is safe. 0 of 24 tested contaminants exceeded recommended levels. Water is supplied by Affinity Water.
What contaminants are in CM18 water?
We tested 24 contaminants in CM18 water. None exceeded recommended safe levels.
Who supplies water in CM18?
CM18 (Harlow) is supplied by Affinity Water. You can view their full profile and compliance data on our supplier page.
Is CM18 water hard or soft?
Water in CM18 (Harlow) has a hardness of 317 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 CM18?
CM18 water scored 9.3/10 with no contaminants above recommended levels. A filter is optional but can improve taste, especially if you notice a chlorine flavour. See our filter recommendations for your area.
Are there PFAS forever chemicals in CM18 water?
No PFAS (forever chemicals) result is attached to the tap-water tests for CM18, 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 CM18?
The Environment Agency rated the Cannons Brook as bad for ecological health in its 2025 assessment, meaning the river is severely damaged, with most of the expected wildlife missing. It is held back by insects and other small river life, water plants and algae 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. Its ecological rating has dropped since the previous assessment. This is a rating of the river, not of tap water in CM18, 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?
- Is UK Tap Water Safe?Everything you need to know about tap water safety in the UK
- 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
How to test your waterBest water filtersFilter shower headsWater testing kitsUK water rankingsWater hardness checkerWater hardness map
River and groundwater readings near CM18
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 CM18.