Tap water in SO20, Test ValleySafe to drink.Very hard.
Supplied by Southern Water. 10,300 samples, 23 substances, latest on 17 April 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 SO20.
Osmio PRO-III Ultimate Whole House
£499typical price
Removes nitrate, the result that stood out in SO20.
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What's in a glass of SO20 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. 18 of 19 substances used under a quarter of theirs.
- Nitrate86%
- Colour15%
- Trihalomethanes9%
- Nickel7%
- Aluminium6%
- Copper5%
- Ammonia5%
- Iron5%
- Lead4%
- Mercury4%
- Manganese4%
- Turbidity3%
- Arsenic2%
- Nitrite2%
- Bromate1%
- Selenium1%
- Antimony<1%
- Cadmium<1%
- Chromium<1%
- pH 7.2 pH
- Coliform Bacteria none found
- E. coli none found
- Conductivity 541 µS/cm
All 23 results as a table
| Substance | Result | Legal limit | Share of limit |
|---|---|---|---|
| Nitrate | 43.1 mg/L | 50 mg/L | 86% |
| Iron | 0.00928 mg/L | 0.2 mg/L | 5% |
| Colour | 3 mg/L Pt/Co | 20 mg/L Pt/Co | 15% |
| Turbidity | 0.13 NTU | 4 NTU | 3% |
| pH | 7.2 pH | No legal limit | – |
| Ammonia | 0.025 mg/L | 0.5 mg/L | 5% |
| Aluminium | 0.0113 mg/L | 0.2 mg/L | 6% |
| Manganese | 0.00178 mg/L | 0.05 mg/L | 4% |
| Copper | 0.109 mg/L | 2 mg/L | 5% |
| Lead | 0.00041 mg/L | 0.01 mg/L | 4% |
| Coliform Bacteria | 0 count/100ml | Must be zero | None found |
| E. coli | 0 count/100ml | Must be zero | None found |
| Conductivity | 541 µS/cm | No legal limit | – |
| Trihalomethanes | 0.00897 mg/L | 0.1 mg/L | 9% |
| Nitrite | 0.009 mg/L | 0.5 mg/L | 2% |
| Arsenic | 0.0002 mg/L | 0.01 mg/L | 2% |
| Cadmium | 0.000031 mg/L | 0.005 mg/L | <1% |
| Chromium | 0.00019 mg/L | 0.05 mg/L | <1% |
| Nickel | 0.00138 mg/L | 0.02 mg/L | 7% |
| Antimony | 0.000043 mg/L | 0.005 mg/L | <1% |
| Selenium | 0.00043 mg/L | 0.04 mg/L | 1% |
| Mercury | 0.00004 mg/L | 0.001 mg/L | 4% |
| Bromate | 0.00013 mg/L | 0.01 mg/L | 1% |
276mg of limescale minerals in every litre, typical for the SO area. SO20 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 SO20
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Your river is the Test - conf Anton to conf Dun, rated good
The Environment Agency rated the Test - conf Anton to conf Dun 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
SO20 in short
Tap water in SO20 (Test Valley) is supplied by Southern Water in the Test Valley Central zone and scores 9.3 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 17 April 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
- 2nd cleanest of 5 areas tested in Test ValleyOnly 1 area in Test Valley scored higher. The best is SP10 on 9.4.
Questions about SO20 water
Is SO20 tap water safe to drink?
Based on the latest tests, SO20 (Test Valley) water scores 9.3/10, which is safe. 1 of 23 tested contaminants exceeded recommended levels. Water is supplied by Southern Water.
What contaminants are in SO20 water?
We tested 23 contaminants in SO20 water. 1 were flagged, including Nitrate.
Who supplies water in SO20?
SO20 (Test Valley) is supplied by Southern Water. You can view their full profile and compliance data on our supplier page.
Is SO20 water hard or soft?
No hardness reading has been published for SO20 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 SO20?
With 1 contaminant above recommended levels in SO20, a water filter could help. A filter jug or under-sink filter can reduce most common contaminants. See our filter recommendations for your area.
Are there PFAS forever chemicals in SO20 water?
No PFAS (forever chemicals) result is attached to the tap-water tests for SO20, and the Environment Agency has no PFAS detections in rivers or groundwater within 10 km of it. That reflects where sampling has happened as much as the water itself.
How clean is the river near SO20?
The Environment Agency rated the Test - conf Anton to conf Dun 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 SO20, which is treated before it reaches homes.
Keep reading
- 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
Nitrate levelsHow to test your waterBest water filtersFilter shower headsWater testing kitsUK water rankingsWater hardness checkerWater hardness map
River and groundwater readings near SO20
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 SO20.