Tap water in SO23, WinchesterSafe to drink.Very hard.
Supplied by Southern Water. 14,740 samples, 23 substances, latest on 27 April 2026. Everything is inside the legal limit, and nothing comes close to it.
9.3 / 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 276 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 SO23 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.
Nitrate came closest to a limit, at 68% of it. 18 of 19 substances used under a quarter of theirs.
- Nitrate68%
- Trihalomethanes19%
- Ammonia17%
- Colour15%
- Fluoride6%
- Aluminium6%
- Nickel5%
- Iron5%
- Manganese4%
- Turbidity3%
- Lead3%
- Nitrite2%
- Copper2%
- Arsenic1%
- Bromate1%
- Antimony1%
- Selenium1%
- Cadmium<1%
- Chromium<1%
- Coliform Bacteria none found
- E. coli none found
- pH 8 pH
- Conductivity 551 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 | 3 mg/L Pt/Co | 20 mg/L Pt/Co | 15% |
| Turbidity | 0.13 NTU | 4 NTU | 3% |
| pH | 8 pH | No legal limit | – |
| Nitrate | 34.1 mg/L | 50 mg/L | 68% |
| Aluminium | 0.0113 mg/L | 0.2 mg/L | 6% |
| Iron | 0.00928 mg/L | 0.2 mg/L | 5% |
| Manganese | 0.00178 mg/L | 0.05 mg/L | 4% |
| Lead | 0.00026 mg/L | 0.01 mg/L | 3% |
| Conductivity | 551 µS/cm | No legal limit | – |
| Trihalomethanes | 0.0188 mg/L | 0.1 mg/L | 19% |
| Nitrite | 0.009 mg/L | 0.5 mg/L | 2% |
| Ammonia | 0.086 mg/L | 0.5 mg/L | 17% |
| Copper | 0.033 mg/L | 2 mg/L | 2% |
| Arsenic | 0.00014 mg/L | 0.01 mg/L | 1% |
| Cadmium | 0.000031 mg/L | 0.005 mg/L | <1% |
| Chromium | 0.00019 mg/L | 0.05 mg/L | <1% |
| Nickel | 0.00103 mg/L | 0.02 mg/L | 5% |
| Antimony | 0.000062 mg/L | 0.005 mg/L | 1% |
| Selenium | 0.00046 mg/L | 0.04 mg/L | 1% |
| Bromate | 0.00013 mg/L | 0.01 mg/L | 1% |
| Fluoride | 0.09 mg/L | 1.5 mg/L | 6% |
276mg of limescale minerals in every litre, typical for the SO area. SO23 has no reading of its own.
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 SO23
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Your river is the Nun's Walk Stream, rated moderate
The Environment Agency rated the Nun's Walk Stream as moderate for ecological health in its 2025 assessment, meaning the river is noticeably changed by pollution or engineering. It is held back by fish. 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
18
forever-chemical detections in nearby rivers and groundwater
At 1 site. The highest was PFBA at 0.0018 µg/L, at RSN0121 Monks Brook Downstream of A3090, 9.3 km away, in April 2023. These are river and borehole samples, not tests of your tap water.
Every PFAS sample around Southampton · Which filters remove PFAS · PFAS explained
SO23 in short
Tap water in SO23 (Winchester) is supplied by Southern Water in the Winchester Central zone and scores 9.3 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 27 April 2026.
- Nitrate is the reading closest to its limit, at 68% of the 50 mg/L maximumIt passed with room to spare, and everything else tested sat further below its limit. See every reading
- Very hard water at 276 mg/LThe threshold for very hard is 250 mg/L. Expect visible limescale on taps and in kettles across the SO postcode area. How hardness is measured
- 3rd cleanest of 7 areas tested in WinchesterOnly 2 areas in Winchester scored higher. The best is SO21 on 9.3.
Questions about SO23 water
Is SO23 tap water safe to drink?
Based on the latest tests, SO23 (Winchester) water scores 9.3/10, which is safe. 0 of 23 tested contaminants exceeded recommended levels. Water is supplied by Southern Water.
What contaminants are in SO23 water?
We tested 23 contaminants in SO23 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 SO23?
SO23 (Winchester) is supplied by Southern Water. You can view their full profile and compliance data on our supplier page.
Is SO23 water hard or soft?
No hardness reading has been published for SO23 itself. Across the SO postcode area the typical value is 276 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 SO23?
SO23 water scored 9.3/10 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 SO23 water?
The tap-water tests we hold for SO23 do not include a PFAS result. Environment Agency monitoring found PFAS in 18 river and groundwater samples from 1 sites within 10 km of SO23, the highest being PFBA at 0.0018 µg/L about 9.3 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 SO23?
The Environment Agency rated the Nun's Walk Stream as moderate for ecological health in its 2025 assessment, meaning the river is noticeably changed by pollution or engineering. It is held back by fish. 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 SO23, 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 kitsUK water rankingsWater hardness checkerWater hardness map
River and groundwater readings near SO23
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 SO23.