Tap water in OX4, OxfordSafe to drink.Very hard.
Supplied by Thames Water. 74 samples, 23 substances, latest on 31 December 2025. Everything is inside the legal limit, and nothing comes close to it.
8.9 / 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 241 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 OX4 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 72% of it. 17 of 19 substances used under a quarter of theirs.
- Nitrite72%
- Nitrate36%
- Trihalomethanes13%
- Bromate10%
- Lead9%
- Colour9%
- Nickel9%
- Fluoride8%
- Cadmium8%
- Mercury7%
- Arsenic7%
- Antimony6%
- Chromium5%
- Aluminium5%
- Boron4%
- Iron3%
- Manganese2%
- Copper2%
- Selenium1%
- Coliform Bacteria none found
- E. coli none found
- Conductivity 507 µS/cm
All 23 results as a table
| Substance | Result | Legal limit | Share of limit |
|---|---|---|---|
| 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 | 507 µS/cm | No legal limit | – |
| Fluoride | 0.12 mg/L | 1.5 mg/L | 8% |
| Nitrate | 17.9 mg/L | 50 mg/L | 36% |
| Nitrite | 0.36 mg/L | 0.5 mg/L | 72% |
| Hardness (as CaCO3) | 241 mg/L | No legal limit | – |
| Aluminium | 0.0099 mg/L | 0.2 mg/L | 5% |
| Antimony | 0.0003 mg/L | 0.005 mg/L | 6% |
| Arsenic | 0.0007 mg/L | 0.01 mg/L | 7% |
| Boron | 0.04 mg/L | 1 mg/L | 4% |
| Cadmium | 0.0004 mg/L | 0.005 mg/L | 8% |
| Chromium | 0.0025 mg/L | 0.05 mg/L | 5% |
| Copper | 0.03 mg/L | 2 mg/L | 2% |
| Iron | 0.007 mg/L | 0.2 mg/L | 3% |
| Lead | 0.0009 mg/L | 0.01 mg/L | 9% |
| Manganese | 0.0008 mg/L | 0.05 mg/L | 2% |
| Mercury | 0.00007 mg/L | 0.001 mg/L | 7% |
| Nickel | 0.0017 mg/L | 0.02 mg/L | 9% |
| Selenium | 0.0004 mg/L | 0.04 mg/L | 1% |
| Trihalomethanes | 0.013 mg/L | 0.1 mg/L | 13% |
| Bromate | 0.001 mg/L | 0.01 mg/L | 10% |
241mg 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 OX4
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Your river is the Thames (Evenlode to Thame), rated poor
The Environment Agency rated the Thames (Evenlode to Thame) as poor for ecological health in its 2025 assessment, meaning the river is badly affected, with much of the expected wildlife missing. It is held back by fish 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
487
forever-chemical detections in nearby rivers and groundwater
At 13 sites. The highest was PFBS at 0.069 µg/L, at Cherwell at Marston Road, Oxford, 3.2 km away, in September 2023. These are river and borehole samples, not tests of your tap water.
Every PFAS sample around Oxford · Which filters remove PFAS · PFAS explained
OX4 in short
Tap water in OX4 (Oxford) is supplied by Thames Water in the Oxford Central zone and scores 8.9 out of 10, against an England and Wales average of 9.0. None of the 23 tested substances came close to a limit. The latest sample is from 31 December 2025.
- The cleanest tap water of the 4 areas tested in OxfordOX4 scores 8.9 out of 10, ahead of OX1 in second place on 8.7. Every area in Oxford
- Nitrite is the reading closest to its limit, at 72% of the 0.5 mg/L maximumIt passed with room to spare, and everything else tested sat further below its limit. See every reading
- Scores higher than all 3 neighbouring districtsThe nearest rival is OX1 on 8.7, against 8.9 here. Compare with OX1
Questions about OX4 water
Is OX4 tap water safe to drink?
Based on the latest tests, OX4 (Oxford) water scores 8.9/10, which is safe. 0 of 23 tested contaminants exceeded recommended levels. Water is supplied by Thames Water.
What contaminants are in OX4 water?
We tested 23 contaminants in OX4 water. None exceeded recommended safe levels. 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 OX4?
OX4 (Oxford) is supplied by Thames Water. You can view their full profile and compliance data on our supplier page.
Is OX4 water hard or soft?
Water in OX4 (Oxford) has a hardness of 241 mg/L CaCO3, which is classified as hard. Hard water can cause limescale buildup. A water softener or filter jug may help.
Should I use a water filter in OX4?
OX4 water scored 8.9/10 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 OX4 water?
The tap-water tests we hold for OX4 do not include a PFAS result. Environment Agency monitoring found PFAS in 487 river and groundwater samples from 13 sites within 10 km of OX4, the highest being PFBS at 0.069 µg/L about 3.2 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 OX4?
The Environment Agency rated the Thames (Evenlode to Thame) as poor for ecological health in its 2025 assessment, meaning the river is badly affected, with much of the expected wildlife missing. It is held back by fish 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 OX4, 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?
- 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 kitsAll of OxfordUK water rankingsWater hardness checkerWater hardness map
River and groundwater readings near OX4
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 OX4.