Tap water in SO25, WinchesterSafe to drink.Very hard.
Supplied by Southern Water. 1,438 samples, 21 substances, latest on 20 March 2026. Everything is inside the legal limit. One result, nitrate, sits close to the line.
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.
Waterdrop G3P600 Reverse Osmosis
£550typical price
Removes nitrate, the result that stood out in SO25.
Osmio PRO-III Ultimate Whole House
£499typical price
Removes nitrate, the result that stood out in SO25.
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What's in a glass of SO25 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 86% of it. 16 of 17 substances used under a quarter of theirs.
- Nitrate86%
- Colour15%
- Nickel6%
- Aluminium6%
- Ammonia5%
- Iron5%
- Trihalomethanes4%
- Copper4%
- Manganese4%
- Turbidity3%
- Lead2%
- Nitrite2%
- Arsenic1%
- Antimony1%
- Selenium1%
- Cadmium<1%
- Chromium<1%
- Coliform Bacteria none found
- E. coli none found
- Conductivity 552 µS/cm
- pH 7.3 pH
All 21 results as a table
| Substance | Result | Legal limit | Share of limit |
|---|---|---|---|
| Nitrate | 43.1 mg/L | 50 mg/L | 86% |
| 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 | 0.00018 mg/L | 0.01 mg/L | 2% |
| Coliform Bacteria | 0 count/100ml | Must be zero | None found |
| E. coli | 0 count/100ml | Must be zero | None found |
| Conductivity | 552 µS/cm | No legal limit | – |
| Colour | 3 mg/L Pt/Co | 20 mg/L Pt/Co | 15% |
| Turbidity | 0.13 NTU | 4 NTU | 3% |
| pH | 7.3 pH | No legal limit | – |
| Nitrite | 0.009 mg/L | 0.5 mg/L | 2% |
| Ammonia | 0.025 mg/L | 0.5 mg/L | 5% |
| Copper | 0.0733 mg/L | 2 mg/L | 4% |
| 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 | 0.00124 mg/L | 0.02 mg/L | 6% |
| Antimony | 0.000062 mg/L | 0.005 mg/L | 1% |
| Selenium | 0.00047 mg/L | 0.04 mg/L | 1% |
| Trihalomethanes | 0.0044 mg/L | 0.1 mg/L | 4% |
276mg of limescale minerals in every litre, typical for the SO area. SO25 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 SO25
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Your river is the Itchen, rated good
The Environment Agency rated the Itchen as good for ecological health in its 2025 assessment, meaning the river is only slightly changed from its natural state. 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
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, 9.8 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
SO25 in short
Tap water in SO25 (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. 1 of 21 tested substances was close to or over a limit. The latest sample is from 20 March 2026.
- Nitrate is within its legal limit but flagged, at 86% of the 50 mg/L maximumAnything over three quarters of a limit is flagged here as worth watching. It has not gone over. 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
- 4th cleanest of 7 areas tested in WinchesterSquarely mid-table for Winchester, between SO21 on 9.3 and SO24 on 9.2.
Questions about SO25 water
Is SO25 tap water safe to drink?
Based on the latest tests, SO25 (Winchester) water scores 9.3/10, which is safe. 1 of 21 tested contaminants exceeded recommended levels. Water is supplied by Southern Water.
What contaminants are in SO25 water?
We tested 21 contaminants in SO25 water. 1 were flagged, including Nitrate. 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 SO25?
SO25 (Winchester) is supplied by Southern Water. You can view their full profile and compliance data on our supplier page.
Is SO25 water hard or soft?
No hardness reading has been published for SO25 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 SO25?
With 1 contaminant above recommended levels in SO25, 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 SO25 water?
The tap-water tests we hold for SO25 do not include a PFAS result. Environment Agency monitoring found PFAS in 18 river and groundwater samples from 1 sites within 10 km of SO25, the highest being PFBA at 0.0018 µg/L about 9.8 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 SO25?
The Environment Agency rated the Itchen as good for ecological health in its 2025 assessment, meaning the river is only slightly changed from its natural state. 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 SO25, 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 SO25
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 SO25.