Tap water in AL6, Welwyn HatfieldToo few tap tests to call it.Very hard.
Supplied by Thames Water. 14 substances, latest on 4 September 2026. These are river and groundwater samples near AL6, not tests of treated tap water, so treat the score as a rough guide.
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 319 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
We earn a commission if you buy through these links, at no extra cost to you. It never changes which product we put first. How we make money
What's in a glass of AL6 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.
Iron came closest to a limit, at 43% of it. 6 of 7 substances used under a quarter of theirs.
- Iron43%
- Nickel17%
- Nitrate14%
- Manganese7%
- Nitrite3%
- Lead2%
- Copper<1%
- pH 7.76 pH
- Temperature 16.5 °C
- Conductivity 633 µS/cm
- Phosphate 0.17 mg/L
- Dissolved Oxygen 8.9 mg/L
- Zinc 0.001 mg/L
- PFAS (total) 0.00075 µg/L
All 14 results as a table
| Substance | Result | Legal limit | Share of limit |
|---|---|---|---|
| pH | 7.76 pH | No legal limit | – |
| Temperature | 16.5 °C | No legal limit | – |
| Conductivity | 633 µS/cm | No legal limit | – |
| Nitrate | 7 mg/L | 50 mg/L | 14% |
| Nitrite | 0.015 mg/L | 0.5 mg/L | 3% |
| Phosphate | 0.17 mg/L | No legal limit | – |
| Dissolved Oxygen | 8.9 mg/L | No legal limit | – |
| Iron | 0.085 mg/L | 0.2 mg/L | 43% |
| Manganese | 0.0035 mg/L | 0.05 mg/L | 7% |
| Copper | 0.00026 mg/L | 2 mg/L | <1% |
| Zinc | 0.001 mg/L | No legal limit | – |
| Lead | 0.0002 mg/L | 0.01 mg/L | 2% |
| Nickel | 0.0034 mg/L | 0.02 mg/L | 17% |
| PFAS (total) | 0.00075 µg/L | No legal limit | – |
319mg 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 AL6
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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
AL6 in short
Tap water in AL6 (Welwyn Hatfield) is supplied by Thames Water in the Welwyn Hatfield Central zone and scores 9.0 out of 10, against an England and Wales average of 9.0. None of the 14 tested substances came close to a limit. The latest sample is from 4 September 2026.
- The cleanest tap water of the 5 areas tested in Welwyn HatfieldAL6 scores 9 out of 10, ahead of AL7 in second place on 8.6.
- Among the hardest water in the country at 319 mg/LVery hard starts at 250 mg/L. At this level kettles scale up within weeks and a softener is a normal purchase in AL6. How hardness is measured
- Iron is the reading closest to its limit, at 43% of the 0.2 mg/L maximumIt passed with room to spare, and everything else tested sat further below its limit. See every reading
Questions about AL6 water
Is AL6 tap water safe to drink?
Based on the latest tests, AL6 (Welwyn Hatfield) water scores 9/10, which is safe. 0 of 14 tested contaminants exceeded recommended levels. Water is supplied by Thames Water.
What contaminants are in AL6 water?
We tested 14 contaminants in AL6 water. None exceeded recommended safe levels. PFAS (forever chemicals) were also detected at 0.00075 µg/L in nearby environmental monitoring.
Who supplies water in AL6?
AL6 (Welwyn Hatfield) is supplied by Thames Water. You can view their full profile and compliance data on our supplier page.
Is AL6 water hard or soft?
Water in AL6 (Welwyn Hatfield) has a hardness of 319 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 AL6?
AL6 water scored 9/10 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 AL6 water?
Yes, PFAS (per- and polyfluoroalkyl substances) have been detected in AL6 at 0.00075 µg/L from environmental monitoring. The UK currently has no legal limit for PFAS in drinking water. Reverse osmosis and activated carbon filters can reduce PFAS levels.
How clean is the river near AL6?
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 AL6, 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
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- 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?
- 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 explainedHow to test your waterBest water filtersFilter shower headsWater testing kitsUK water rankingsWater hardness checkerWater hardness map
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