Tap water in TW3, HounslowNitrite is over the limit.Very hard.
Supplied by Thames Water. 74 samples, 23 substances, latest on 31 December 2025. Nitrite came in above the legal limit. Everything else passed.
8.5 / 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 274 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
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 TW3 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%
- Nitrate56%
- Bromate15%
- Trihalomethanes14%
- Lead12%
- Arsenic10%
- Colour10%
- Fluoride9%
- Cadmium8%
- Mercury7%
- Antimony6%
- Boron5%
- Chromium5%
- Aluminium4%
- Nickel4%
- Iron3%
- Selenium1%
- Manganese1%
- Copper1%
- Coliform Bacteria none found
- E. coli none found
- Conductivity 577 µS/cm
All 23 results as a table
| Substance | Result | Legal limit | Share of limit |
|---|---|---|---|
| Nitrite | 0.61 mg/L | 0.5 mg/L | 122% |
| Coliform Bacteria | 0 count/100ml | Must be zero | None found |
| E. coli | 0 count/100ml | Must be zero | None found |
| Colour | 1.9 mg/L Pt/Co | 20 mg/L Pt/Co | 10% |
| Conductivity | 577 µS/cm | No legal limit | – |
| Fluoride | 0.14 mg/L | 1.5 mg/L | 9% |
| Nitrate | 27.8 mg/L | 50 mg/L | 56% |
| Hardness (as CaCO3) | 274 mg/L | No legal limit | – |
| Aluminium | 0.0087 mg/L | 0.2 mg/L | 4% |
| Antimony | 0.0003 mg/L | 0.005 mg/L | 6% |
| Arsenic | 0.001 mg/L | 0.01 mg/L | 10% |
| 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 | 0.0012 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 | 0.0008 mg/L | 0.02 mg/L | 4% |
| Selenium | 0.0005 mg/L | 0.04 mg/L | 1% |
| Trihalomethanes | 0.014 mg/L | 0.1 mg/L | 14% |
| Bromate | 0.0015 mg/L | 0.01 mg/L | 15% |
274mg 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 TW3
Leave your details and we will email you when we can match you with installers who cover TW3. No obligation.
Request a free assessment and we'll come back to you with local installer options for your area.
100%
free, no obligation
shared only with your consent
Your river is the Crane, rated moderate
The Environment Agency rated the Crane as moderate for ecological health in its 2025 assessment, meaning the river is noticeably changed by pollution or engineering. It is held back by 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
885
forever-chemical detections in nearby rivers and groundwater
At 5 sites. The highest was 6:2 FtSAB at 0.099 µg/L, at Crane at Northcote Road, Isleworth, 2.7 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
TW3 in short
Tap water in TW3 (Hounslow) is supplied by Thames Water in the Hounslow Central zone and scores 8.5 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 was measured at 0.61 mg/L, 22% over the UK limitIt is the only one of 23 tested substances to go over its limit. See the full results
- Very hard water at 274 mg/LThe threshold for very hard is 250 mg/L. Expect visible limescale on taps and in kettles in TW3. How hardness is measured
- 3rd cleanest of 8 areas tested in HounslowOnly 2 areas in Hounslow scored higher. The best is TW7 on 8.6.
Questions about TW3 water
Is TW3 tap water safe to drink?
Based on the latest tests, TW3 (Hounslow) water scores 8.5/10, which is safe. 1 of 23 tested contaminants exceeded recommended levels. Water is supplied by Thames Water.
What contaminants are in TW3 water?
We tested 23 contaminants in TW3 water. 1 were flagged, including 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 TW3?
TW3 (Hounslow) is supplied by Thames Water. You can view their full profile and compliance data on our supplier page.
Is TW3 water hard or soft?
Water in TW3 (Hounslow) has a hardness of 274 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 TW3?
With 1 contaminant above recommended levels in TW3, 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 TW3 water?
The tap-water tests we hold for TW3 do not include a PFAS result. Environment Agency monitoring found PFAS in 885 river and groundwater samples from 5 sites within 10 km of TW3, the highest being 6:2 FtSAB at 0.099 µg/L about 2.7 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 TW3?
The Environment Agency rated the Crane as moderate for ecological health in its 2025 assessment, meaning the river is noticeably changed by pollution or engineering. It is held back by 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 TW3, 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 TW3
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 |
|---|---|---|
| pH | 8.02 pH | None |
| Temperature | 21.5 °C | None |
| Conductivity | 889 µS/cm | None |
| Ammonia | 0.066 mg/L | 0.5 mg/L |
| Nitrate | 3 mg/L | 50 mg/L |
| Nitrite | 0.0072 mg/L | 0.5 mg/L |
| Phosphate | 0.25 mg/L | None |
| Dissolved Oxygen | 8.2 mg/L | None |
| Lead | 0.001 mg/L | 0.01 mg/L |
| Cadmium | 0.000019 mg/L | 0.005 mg/L |
| Copper | 0.0018 mg/L | 2 mg/L |
| Zinc | 0.0069 mg/L | None |
| Nickel | 0.0035 mg/L | 0.02 mg/L |
| PFAS (total) | 0.047 µg/L | None |
Get alerts for your area
We'll email you when water quality data changes for TW3.