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tapwater
England and Wales average 9.0

Tap water in GU23, GuildfordSafe to drink.Slightly hard.

Supplied by Thames Water. 71 samples, 23 substances, latest on 31 December 2025. Everything is inside the legal limit, and nothing comes close to it.

See the filter we recommendSee everything that was tested

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

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Households concerned about PFAS and heavy metals

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Basic chlorine and taste improvement on a budget

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What's in a glass of GU23 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 came closest to a limit, at 14% of it. 19 of 19 substances used under a quarter of theirs.

0%25%50%75%limitLegal limitSelenium: 0.0004 mg/L, 1% of the 0.04 mg/L limitSelenium1%Manganese: 0.0007 mg/L, 1% of the 0.05 mg/L limitManganese1%Boron: 0.02 mg/L, 2% of the 1 mg/L limitBoron2%Trihalomethanes: 0.002 mg/L, 2% of the 0.1 mg/L limitTrihalomethanes2%Copper: 0.07 mg/L, 4% of the 2 mg/L limitCopper4%Aluminium: 0.0082 mg/L, 4% of the 0.2 mg/L limitAluminium4%Chromium: 0.0025 mg/L, 5% of the 0.05 mg/L limitChromium5%Antimony: 0.0003 mg/L, 6% of the 0.005 mg/L limitAntimony6%Nitrate: 3.1 mg/L, 6% of the 50 mg/L limitNitrate6%Mercury: 0.00007 mg/L, 7% of the 0.001 mg/L limitMercury7%Arsenic: 0.0007 mg/L, 7% of the 0.01 mg/L limitArsenic7%Iron: 0.015 mg/L, 8% of the 0.2 mg/L limitIron8%Fluoride: 0.12 mg/L, 8% of the 1.5 mg/L limitFluoride8%Cadmium: 0.0004 mg/L, 8% of the 0.005 mg/L limitCadmium8%Colour: 1.8 mg/L Pt/Co, 9% of the 20 mg/L Pt/Co limitColour9%Bromate: 0.001 mg/L, 10% of the 0.01 mg/L limitBromate10%Nickel: 0.0024 mg/L, 12% of the 0.02 mg/L limitNickel12%Lead: 0.0013 mg/L, 13% of the 0.01 mg/L limitLead13%Nitrite: 0.07 mg/L, 14% of the 0.5 mg/L limitNitrite14%
  1. Nitrite14%
  2. Lead13%
  3. Nickel12%
  4. Bromate10%
  5. Colour9%
  6. Fluoride8%
  7. Cadmium8%
  8. Iron8%
  9. Mercury7%
  10. Arsenic7%
  11. Nitrate6%
  12. Antimony6%
  13. Chromium5%
  14. Aluminium4%
  15. Copper4%
  16. Boron2%
  17. Trihalomethanes2%
  18. Manganese1%
  19. Selenium1%
  • Coliform Bacteria none found
  • E. coli none found
  • Conductivity 287 µS/cm
All 23 results as a table
SubstanceResultLegal limitShare of limit
Coliform Bacteria0 count/100mlMust be zeroNone found
E. coli0 count/100mlMust be zeroNone found
Colour1.8 mg/L Pt/Co20 mg/L Pt/Co
9%
Conductivity287 µS/cmNo legal limit–
Fluoride0.12 mg/L1.5 mg/L
8%
Nitrate3.1 mg/L50 mg/L
6%
Nitrite0.07 mg/L0.5 mg/L
14%
Hardness (as CaCO3)154 mg/LNo legal limit–
Aluminium0.0082 mg/L0.2 mg/L
4%
Antimony0.0003 mg/L0.005 mg/L
6%
Arsenic0.0007 mg/L0.01 mg/L
7%
Boron0.02 mg/L1 mg/L
2%
Cadmium0.0004 mg/L0.005 mg/L
8%
Chromium0.0025 mg/L0.05 mg/L
5%
Copper0.07 mg/L2 mg/L
4%
Iron0.015 mg/L0.2 mg/L
8%
Lead0.0013 mg/L0.01 mg/L
13%
Manganese0.0007 mg/L0.05 mg/L
1%
Mercury0.00007 mg/L0.001 mg/L
7%
Nickel0.0024 mg/L0.02 mg/L
12%
Selenium0.0004 mg/L0.04 mg/L
1%
Trihalomethanes0.002 mg/L0.1 mg/L
2%
Bromate0.001 mg/L0.01 mg/L
10%

154mg of limescale minerals in every litre

Middling hardness. Some scale, slowly

Below the point where a softener pays for itself. Descaling the kettle now and then is all most homes need.

Soft400 mg/L
Outside your tap

Your river is the East Clandon Stream, rated moderate

The Environment Agency rated the East Clandon 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 insects and other small river life, water plants and algae and 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

GU23 in short

Tap water in GU23 (Guildford) is supplied by Thames Water in the Guildford Central zone and scores 9.4 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 31 December 2025.

  • 3rd cleanest of 7 areas tested in GuildfordOnly 2 areas in Guildford scored higher. The best is GU12 on 9.4.
  • Nothing tested came within 40% of its legal limitThe highest was Nitrite at 14% of the 0.5 mg/L maximum. See every reading
  • Moderately hard water at 154 mg/LSome scale over time in GU23, but not enough to justify a softener for most homes. How hardness is measured

Next door

KT249.4 out of 10 · 154 mg/LGU18.8 out of 10 · 204 mg/LGU29.4 out of 10 · 154 mg/LGU38.8 out of 10 · 138 mg/LGU49.1 out of 10 · 75 mg/LGU129.4 out of 10 · 154 mg/LKT148.8 out of 10 · 141 mg/LGU228.8 out of 10 · 204 mg/L

Questions about GU23 water

Is GU23 tap water safe to drink?

Based on the latest tests, GU23 (Guildford) water scores 9.4/10, which is safe. 0 of 23 tested contaminants exceeded recommended levels. Water is supplied by Thames Water.

What contaminants are in GU23 water?

We tested 23 contaminants in GU23 water. None exceeded recommended safe levels.

Who supplies water in GU23?

GU23 (Guildford) is supplied by Thames Water. You can view their full profile and compliance data on our supplier page.

Is GU23 water hard or soft?

Water in GU23 (Guildford) has a hardness of 154 mg/L CaCO3, which is classified as moderately hard. This is a moderate hardness level.

Should I use a water filter in GU23?

GU23 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 GU23 water?

No PFAS (forever chemicals) result is attached to the tap-water tests for GU23, 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 GU23?

The Environment Agency rated the East Clandon 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 insects and other small river life, water plants and algae and 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 GU23, which is treated before it reaches homes.

Keep reading

How to test your waterBest water filtersFilter shower headsWater testing kitsUK water rankingsWater hardness checkerWater hardness map

River and groundwater readings near GU23

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.

SubstanceReadingDrinking water limit
Iron0.244 mg/L0.2 mg/L
pH8.38 pHNone
Temperature21.8 °CNone
Conductivity526 µS/cmNone
Ammonia0.031 mg/L0.5 mg/L
Nitrate8.6 mg/L50 mg/L
Nitrite0.024 mg/L0.5 mg/L
Phosphate0.23 mg/LNone
Dissolved Oxygen9.11 mg/LNone
Zinc0.0185 mg/LNone
Copper0.002 mg/L2 mg/L
Manganese0.021 mg/L0.05 mg/L

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Source: Thames Water test results, published through the Stream Water Data Portal; rivers and PFAS from the Environment Agency. Page updated . How we score · Where the data comes from