Tap water in HA7, Harrow2 results are over the limit.Very hard.
Supplied by Thames Water. 74 samples, 23 substances, latest on 31 December 2025. Coliform Bacteria and Nitrite came in above the legal limit. Everything else passed.
7.7 / 10
The tank is as full as the score. The specks are the minerals that make water hard.
What to do about it
Osmio Zero 2.0 Countertop RO
£495typical price
Removes coliform bacteria, the result that stood out in HA7.
Stop the limescale
At 258 mg/L a softener is the only thing that stops limescale. Filters do not soften water.
Osmio PRO-III Ultimate Whole House
£499typical price
Removes coliform bacteria, the result that stood out in HA7.
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What's in a glass of HA7 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 is over its legal limit, at 122% of it.
- Nitrite122%
- Nitrate59%
- Lead30%
- Trihalomethanes18%
- Bromate15%
- Colour10%
- Fluoride9%
- Arsenic9%
- Cadmium8%
- Mercury7%
- Antimony6%
- Boron5%
- Chromium5%
- Nickel5%
- Aluminium4%
- Iron3%
- Manganese1%
- Copper1%
- Selenium1%
- Coliform Bacteria 25 count/100ml found
- E. coli none found
- Conductivity 566 µS/cm
All 23 results as a table
| Substance | Result | Legal limit | Share of limit |
|---|---|---|---|
| Coliform Bacteria | 25 count/100ml | Must be zero | Found |
| Nitrite | 0.61 mg/L | 0.5 mg/L | 122% |
| E. coli | 0 count/100ml | Must be zero | None found |
| Colour | 1.9 mg/L Pt/Co | 20 mg/L Pt/Co | 10% |
| Conductivity | 566 µS/cm | No legal limit | – |
| Fluoride | 0.14 mg/L | 1.5 mg/L | 9% |
| Nitrate | 29.4 mg/L | 50 mg/L | 59% |
| Hardness (as CaCO3) | 258 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 | 0.0009 mg/L | 0.01 mg/L | 9% |
| Boron | 0.05 mg/L | 1 mg/L | 5% |
| Cadmium | 0.0004 mg/L | 0.005 mg/L | 8% |
| Chromium | 0.0025 mg/L | 0.05 mg/L | 5% |
| Copper | 0.02 mg/L | 2 mg/L | 1% |
| Iron | 0.007 mg/L | 0.2 mg/L | 3% |
| Lead | 0.003 mg/L | 0.01 mg/L | 30% |
| Manganese | 0.0006 mg/L | 0.05 mg/L | 1% |
| Mercury | 0.00007 mg/L | 0.001 mg/L | 7% |
| Nickel | 0.0009 mg/L | 0.02 mg/L | 5% |
| Selenium | 0.0004 mg/L | 0.04 mg/L | 1% |
| Trihalomethanes | 0.018 mg/L | 0.1 mg/L | 18% |
| Bromate | 0.0015 mg/L | 0.01 mg/L | 15% |
258mg 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 HA7
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Your river is the Silk Stream and Edgware Brook, rated moderate
The Environment Agency rated the Silk Stream and Edgware Brook as moderate for ecological health in its 2025 assessment, meaning the river is noticeably changed by pollution or engineering. It is held back by insects and other small river life, dissolved oxygen 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
13
forever-chemical detections in nearby rivers and groundwater
At 1 site. The highest was PFOS (total) at 0.0089 µg/L, at Silk Stream at Silk Bridge, A5, Hendon, 5.7 km away, in January 2026. These are river and borehole samples, not tests of your tap water.
Every PFAS sample around London · Which filters remove PFAS · PFAS explained
HA7 in short
Tap water in HA7 (Harrow) is supplied by Thames Water in the Harrow Central zone and scores 7.7 out of 10, against an England and Wales average of 9.0. 2 of 23 tested substances were close to or over a limit. The latest sample is from 31 December 2025.
- Coliform Bacteria detected at 25 per 100 ml, where any amount fails the legal standardAny detection is a failure for this substance. It is one of 2 flagged here. See the full results
- The lowest score of the 5 areas tested in HarrowHA7 scores 7.7 out of 10. The best in Harrow, HA2, scores 8.6.
- Very hard water at 258 mg/LThe threshold for very hard is 250 mg/L. Expect visible limescale on taps and in kettles in HA7. How hardness is measured
Questions about HA7 water
Is HA7 tap water safe to drink?
Based on the latest tests, HA7 (Harrow) water scores 7.7/10, which is safe. 2 of 23 tested contaminants exceeded recommended levels. Water is supplied by Thames Water.
What contaminants are in HA7 water?
We tested 23 contaminants in HA7 water. 2 were flagged, including Coliform Bacteria, Nitrite. 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 HA7?
HA7 (Harrow) is supplied by Thames Water. You can view their full profile and compliance data on our supplier page.
Is HA7 water hard or soft?
Water in HA7 (Harrow) has a hardness of 258 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 HA7?
With 2 contaminants above recommended levels in HA7, 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 HA7 water?
The tap-water tests we hold for HA7 do not include a PFAS result. Environment Agency monitoring found PFAS in 13 river and groundwater samples from 1 sites within 10 km of HA7, the highest being PFOS (total) at 0.0089 µg/L about 5.7 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 HA7?
The Environment Agency rated the Silk Stream and Edgware Brook as moderate for ecological health in its 2025 assessment, meaning the river is noticeably changed by pollution or engineering. It is held back by insects and other small river life, dissolved oxygen 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 HA7, 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 kitsUK water rankingsWater hardness checkerWater hardness map
River and groundwater readings near HA7
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.
| Substance | Reading | Drinking water limit |
|---|---|---|
| Iron | 0.23 mg/L | 0.2 mg/L |
| pH | 7.16 pH | None |
| Temperature | 13.8 °C | None |
| Conductivity | 634 µS/cm | None |
| Hardness (as CaCO3) | 309 mg/L | None |
| Fluoride | 0.63 mg/L | 1.5 mg/L |
| Phosphate | 0.026 mg/L | None |
| Lead | 0.00005 mg/L | 0.01 mg/L |
| Zinc | 0.0075 mg/L | None |
| Nickel | 0.007 mg/L | 0.02 mg/L |
| Manganese | 0.0017 mg/L | 0.05 mg/L |
| Copper | 0.00012 mg/L | 2 mg/L |
| Dissolved Oxygen | 4.32 mg/L | None |
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