Tap water in AL7, Welwyn HatfieldSafe to drink.Very hard.
Supplied by Thames Water. 76 samples, 23 substances, latest on 31 December 2025. Everything is inside the legal limit. One result, nitrite, sits close to the line.
8.6 / 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 289 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 AL7 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 98% of it. 17 of 19 substances used under a quarter of theirs.
- Nitrite98%
- Nitrate49%
- Bromate14%
- Lead12%
- Trihalomethanes10%
- Colour9%
- Cadmium8%
- Mercury7%
- Arsenic7%
- Fluoride7%
- Antimony6%
- Nickel6%
- Chromium5%
- Aluminium4%
- Iron4%
- Copper4%
- Boron2%
- Manganese1%
- Selenium1%
- Coliform Bacteria none found
- E. coli none found
- Conductivity 527 µS/cm
All 23 results as a table
| Substance | Result | Legal limit | Share of limit |
|---|---|---|---|
| Nitrite | 0.49 mg/L | 0.5 mg/L | 98% |
| Coliform Bacteria | 0 count/100ml | Must be zero | None found |
| E. coli | 0 count/100ml | Must be zero | None found |
| Colour | 1.8 mg/L Pt/Co | 20 mg/L Pt/Co | 9% |
| Conductivity | 527 µS/cm | No legal limit | – |
| Fluoride | 0.1 mg/L | 1.5 mg/L | 7% |
| Nitrate | 24.3 mg/L | 50 mg/L | 49% |
| Hardness (as CaCO3) | 274 mg/L | No legal limit | – |
| Aluminium | 0.0082 mg/L | 0.2 mg/L | 4% |
| Antimony | 0.0003 mg/L | 0.005 mg/L | 6% |
| Arsenic | 0.0007 mg/L | 0.01 mg/L | 7% |
| Boron | 0.02 mg/L | 1 mg/L | 2% |
| Cadmium | 0.0004 mg/L | 0.005 mg/L | 8% |
| Chromium | 0.0025 mg/L | 0.05 mg/L | 5% |
| Copper | 0.07 mg/L | 2 mg/L | 4% |
| Iron | 0.008 mg/L | 0.2 mg/L | 4% |
| Lead | 0.0012 mg/L | 0.01 mg/L | 12% |
| Manganese | 0.0006 mg/L | 0.05 mg/L | 1% |
| Mercury | 0.00007 mg/L | 0.001 mg/L | 7% |
| Nickel | 0.0012 mg/L | 0.02 mg/L | 6% |
| Selenium | 0.0004 mg/L | 0.04 mg/L | 1% |
| Trihalomethanes | 0.01 mg/L | 0.1 mg/L | 10% |
| Bromate | 0.0014 mg/L | 0.01 mg/L | 14% |
289mg 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 AL7
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Your river is the Mimram (Codicote Bottom to Lee), rated moderate
The Environment Agency rated the Mimram (Codicote Bottom to Lee) as moderate for ecological health in its 2025 assessment, meaning the river is noticeably changed by pollution or engineering. It is held back by water plants and algae. 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
AL7 in short
Tap water in AL7 (Welwyn Hatfield) is supplied by Thames Water in the Welwyn Hatfield Central zone and scores 8.6 out of 10, against an England and Wales average of 9.0. 1 of 23 tested substances was close to or over a limit. The latest sample is from 31 December 2025.
- Nitrite is within its legal limit but flagged, at 98% 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
- Very hard water at 289 mg/LThe threshold for very hard is 250 mg/L. Expect visible limescale on taps and in kettles in AL7. How hardness is measured
- 2nd cleanest of 5 areas tested in Welwyn HatfieldOnly 1 area in Welwyn Hatfield scored higher. The best is AL6 on 9.
Questions about AL7 water
Is AL7 tap water safe to drink?
Based on the latest tests, AL7 (Welwyn Hatfield) water scores 8.6/10, which is safe. 1 of 23 tested contaminants exceeded recommended levels. Water is supplied by Thames Water.
What contaminants are in AL7 water?
We tested 23 contaminants in AL7 water. 1 were flagged, including Nitrite.
Who supplies water in AL7?
AL7 (Welwyn Hatfield) is supplied by Thames Water. You can view their full profile and compliance data on our supplier page.
Is AL7 water hard or soft?
Water in AL7 (Welwyn Hatfield) has a hardness of 289 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 AL7?
With 1 contaminant above recommended levels in AL7, 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 AL7 water?
No PFAS (forever chemicals) result is attached to the tap-water tests for AL7, 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 AL7?
The Environment Agency rated the Mimram (Codicote Bottom to Lee) as moderate for ecological health in its 2025 assessment, meaning the river is noticeably changed by pollution or engineering. It is held back by water plants and algae. 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 AL7, which is treated before it reaches homes.
Keep reading
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- UK Water Hardness MapIs your water hard or soft, and does it matter?
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- Best water softener UKHarvey, Kinetico, BWT, Monarch and Water2Buy compared
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- 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 AL7
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 AL7.