Tap water in GL51, CheltenhamSafe to drink.Very hard.
Supplied by Severn Trent. 810 samples, 20 substances, latest on 22 December 2025. Everything is inside the legal limit, and nothing comes close to it.
9.4 / 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 258 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 GL51 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.
Trihalomethanes came closest to a limit, at 32% of it. 15 of 17 substances used under a quarter of theirs.
- Trihalomethanes32%
- Nitrate26%
- Aluminium11%
- Nickel5%
- Colour5%
- Iron3%
- Fluoride3%
- Turbidity3%
- Antimony3%
- Nitrite3%
- Arsenic2%
- Manganese1%
- Lead1%
- Copper1%
- Chromium<1%
- Cadmium<1%
- Selenium<1%
- pH 7.5 pH
- Conductivity 344 µS/cm
- Phosphate 1.05 mg/L
All 20 results as a table
| Substance | Result | Legal limit | Share of limit |
|---|---|---|---|
| Iron | 0.007 mg/L | 0.2 mg/L | 3% |
| Colour | 0.9 mg/L Pt/Co | 20 mg/L Pt/Co | 5% |
| Aluminium | 0.021 mg/L | 0.2 mg/L | 11% |
| pH | 7.5 pH | No legal limit | – |
| Turbidity | 0.12 NTU | 4 NTU | 3% |
| Manganese | 0.00073 mg/L | 0.05 mg/L | 1% |
| Conductivity | 344 µS/cm | No legal limit | – |
| Nitrate | 13 mg/L | 50 mg/L | 26% |
| Nitrite | 0.013 mg/L | 0.5 mg/L | 3% |
| Copper | 0.0215 mg/L | 2 mg/L | 1% |
| Fluoride | 0.05 mg/L | 1.5 mg/L | 3% |
| Arsenic | 0.00019 mg/L | 0.01 mg/L | 2% |
| Cadmium | 0.00002 mg/L | 0.005 mg/L | <1% |
| Chromium | 0.00042 mg/L | 0.05 mg/L | <1% |
| Nickel | 0.001 mg/L | 0.02 mg/L | 5% |
| Trihalomethanes | 0.0325 mg/L | 0.1 mg/L | 32% |
| Lead | 0.00014 mg/L | 0.01 mg/L | 1% |
| Antimony | 0.000136 mg/L | 0.005 mg/L | 3% |
| Selenium | 0.00007 mg/L | 0.04 mg/L | <1% |
| Phosphate | 1.05 mg/L | No legal limit | – |
258mg of limescale minerals in every litre, typical for the GL area. GL51 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 GL51
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Your river is the Hatherley Bk - source to conf R Severn, rated moderate
The Environment Agency rated the Hatherley Bk - source to conf R Severn 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
103
forever-chemical detections in nearby rivers and groundwater
At 9 sites. The highest was 6:2 FTSA at 0.017 µg/L, at Brockhampton, Whitehall Farm Spring, 9.4 km away, in June 2023. These are river and borehole samples, not tests of your tap water.
Every PFAS sample around Gloucester · Which filters remove PFAS · PFAS explained
GL51 in short
Tap water in GL51 (Cheltenham) is supplied by Severn Trent in the Cheltenham Central zone and scores 9.4 out of 10, against an England and Wales average of 9.0. None of the 20 tested substances came close to a limit. The latest sample is from 22 December 2025.
- Very hard water at 258 mg/LThe threshold for very hard is 250 mg/L. Expect visible limescale on taps and in kettles across the GL postcode area. How hardness is measured
- 2nd cleanest of 4 areas tested in CheltenhamOnly 1 area in Cheltenham scored higher. The best is GL52 on 9.5. Every area in Cheltenham
- PFAS found at 9 monitoring sites within 10 kmThose are river and groundwater samples, not tap water. The highest was 6:2 FTSA about 9.4 km away. What was measured
Questions about GL51 water
Is GL51 tap water safe to drink?
Based on the latest tests, GL51 (Cheltenham) water scores 9.4/10, which is safe. 0 of 20 tested contaminants exceeded recommended levels. Water is supplied by Severn Trent.
What contaminants are in GL51 water?
We tested 20 contaminants in GL51 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 GL51?
GL51 (Cheltenham) is supplied by Severn Trent. You can view their full profile and compliance data on our supplier page.
Is GL51 water hard or soft?
No hardness reading has been published for GL51 itself. Across the GL postcode area the typical value is 258 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 GL51?
GL51 water scored 9.4/10 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 GL51 water?
The tap-water tests we hold for GL51 do not include a PFAS result. Environment Agency monitoring found PFAS in 103 river and groundwater samples from 9 sites within 10 km of GL51, the highest being 6:2 FTSA at 0.017 µg/L about 9.4 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 GL51?
The Environment Agency rated the Hatherley Bk - source to conf R Severn 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 GL51, 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 CheltenhamUK water rankingsWater hardness checkerWater hardness map
River and groundwater readings near GL51
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 |
|---|---|---|
| Turbidity | 7.2 NTU | 4 NTU |
| pH | 8.24 pH | None |
| Temperature | 16.1 °C | None |
| Conductivity | 986 µS/cm | None |
| Ammonia | 0.068 mg/L | 0.5 mg/L |
| Nitrate | 2.67 mg/L | 50 mg/L |
| Nitrite | 0.0322 mg/L | 0.5 mg/L |
| Phosphate | 0.197 mg/L | None |
| Dissolved Oxygen | 9.36 mg/L | None |
| Hardness (as CaCO3) | 312 mg/L | None |
| Chromium | 0.000933 mg/L | 0.05 mg/L |
| Copper | 0.00145 mg/L | 2 mg/L |
| Nickel | 0.00118 mg/L | 0.02 mg/L |
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