Tap water in SG4, North HertfordshireNitrite is over the limit.Very hard.
Supplied by Affinity Water. 1,336 samples, 24 substances, latest on 19 December 2025. Nitrite came in above the legal limit. Everything else passed.
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 368 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.
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Waterdrop 10UA Under Sink
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What's in a glass of SG4 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 is over its legal limit, at 148% of it.
- Nitrite148%
- Nitrate74%
- Bromate15%
- Ammonia12%
- Colour10%
- Fluoride8%
- Lead7%
- Trihalomethanes5%
- Boron5%
- Iron4%
- Nickel4%
- Turbidity3%
- Mercury2%
- Arsenic2%
- Copper2%
- Cadmium1%
- Aluminium<1%
- Selenium<1%
- Chromium<1%
- Manganese<1%
- Antimony<1%
- E. coli none found
- Coliform Bacteria none found
- Conductivity 504 µS/cm
All 24 results as a table
| Substance | Result | Legal limit | Share of limit |
|---|---|---|---|
| Nitrite | 0.738 mg/L | 0.5 mg/L | 148% |
| Antimony | 0.000031 mg/L | 0.005 mg/L | <1% |
| Lead | 0.000673 mg/L | 0.01 mg/L | 7% |
| E. coli | 0 count/100ml | Must be zero | None found |
| Colour | 2 mg/L Pt/Co | 20 mg/L Pt/Co | 10% |
| Chromium | 0.000383 mg/L | 0.05 mg/L | <1% |
| Turbidity | 0.1 NTU | 4 NTU | 3% |
| Nickel | 0.000866 mg/L | 0.02 mg/L | 4% |
| Coliform Bacteria | 0 count/100ml | Must be zero | None found |
| Aluminium | 0.00199 mg/L | 0.2 mg/L | <1% |
| Iron | 0.00897 mg/L | 0.2 mg/L | 4% |
| Nitrate | 36.9 mg/L | 50 mg/L | 74% |
| Trihalomethanes | 0.0054 mg/L | 0.1 mg/L | 5% |
| Fluoride | 0.121 mg/L | 1.5 mg/L | 8% |
| Ammonia | 0.06 mg/L | 0.5 mg/L | 12% |
| Conductivity | 504 µS/cm | No legal limit | – |
| Manganese | 0.000363 mg/L | 0.05 mg/L | <1% |
| Boron | 0.046 mg/L | 1 mg/L | 5% |
| Cadmium | 0.000054 mg/L | 0.005 mg/L | 1% |
| Mercury | 0.000023 mg/L | 0.001 mg/L | 2% |
| Selenium | 0.000352 mg/L | 0.04 mg/L | <1% |
| Arsenic | 0.000216 mg/L | 0.01 mg/L | 2% |
| Bromate | 0.00147 mg/L | 0.01 mg/L | 15% |
| Copper | 0.038 mg/L | 2 mg/L | 2% |
368mg 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.
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Your river is the Purwell, rated poor
The Environment Agency rated the Purwell 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 water plants and algae. 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
SG4 in short
Tap water in SG4 (North Hertfordshire) is supplied by Affinity Water in the North Hertfordshire Central zone and scores 8.9 out of 10, against an England and Wales average of 9.0. 1 of 24 tested substances was close to or over a limit. The latest sample is from 19 December 2025.
- Nitrite was measured at 0.74 mg/L, 48% over the UK limitIt is the only one of 24 tested substances to go over its limit. See the full results
- Among the hardest water in the country at 368 mg/LVery hard starts at 250 mg/L. At this level kettles scale up within weeks and a softener is a normal purchase in SG4. How hardness is measured
- 4th cleanest of 6 areas tested in North HertfordshireSquarely mid-table for North Hertfordshire, between SG6 on 9.3 and SG8 on 8.8.
Questions about SG4 water
Is SG4 tap water safe to drink?
Based on the latest tests, SG4 (North Hertfordshire) water scores 8.9/10, which is safe. 1 of 24 tested contaminants exceeded recommended levels. Water is supplied by Affinity Water.
What contaminants are in SG4 water?
We tested 24 contaminants in SG4 water. 1 were flagged, including Nitrite.
Who supplies water in SG4?
SG4 (North Hertfordshire) is supplied by Affinity Water. You can view their full profile and compliance data on our supplier page.
Is SG4 water hard or soft?
Water in SG4 (North Hertfordshire) has a hardness of 368 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 SG4?
With 1 contaminant above recommended levels in SG4, 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 SG4 water?
No PFAS (forever chemicals) result is attached to the tap-water tests for SG4, 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 SG4?
The Environment Agency rated the Purwell 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 water plants and algae. 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 SG4, 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 SG4
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 SG4.