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tapwater
England and Wales average 9.0

Tap water in GU3, GuildfordSafe to drink.Slightly hard.

Supplied by Thames Water. 74 samples, 23 substances, latest on 31 December 2025. Everything is inside the legal limit. One result, nitrite, sits close to the line.

See the filter we recommendSee everything that was tested

8.8 / 10

The tank is as full as the score. The specks are the minerals that make water hard.

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What's in a glass of GU3 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 76% of it. 16 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%Copper: 0.03 mg/L, 2% of the 2 mg/L limitCopper2%Boron: 0.03 mg/L, 3% of the 1 mg/L limitBoron3%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%Iron: 0.01 mg/L, 5% of the 0.2 mg/L limitIron5%Antimony: 0.0003 mg/L, 6% of the 0.005 mg/L limitAntimony6%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%Cadmium: 0.0004 mg/L, 8% of the 0.005 mg/L limitCadmium8%Fluoride: 0.13 mg/L, 9% of the 1.5 mg/L limitFluoride9%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: 0.0022 mg/L, 11% of the 0.02 mg/L limitNickel11%Lead: 0.0012 mg/L, 12% of the 0.01 mg/L limitLead12%Nitrate: 18.9 mg/L, 38% of the 50 mg/L limitNitrate38%Trihalomethanes: 0.04 mg/L, 40% of the 0.1 mg/L limitTrihalomethanes40%Nitrite: 0.38 mg/L, 76% of the 0.5 mg/L limitNitrite76%
  1. Nitrite76%
  2. Trihalomethanes40%
  3. Nitrate38%
  4. Lead12%
  5. Nickel11%
  6. Bromate10%
  7. Colour9%
  8. Fluoride9%
  9. Cadmium8%
  10. Mercury7%
  11. Arsenic7%
  12. Antimony6%
  13. Chromium5%
  14. Iron5%
  15. Aluminium4%
  16. Boron3%
  17. Copper2%
  18. Manganese1%
  19. Selenium1%
  • Coliform Bacteria none found
  • E. coli none found
  • Conductivity 363 µS/cm
All 23 results as a table
SubstanceResultLegal limitShare of limit
Nitrite0.38 mg/L0.5 mg/L
76%
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%
Conductivity363 µS/cmNo legal limit–
Fluoride0.13 mg/L1.5 mg/L
9%
Nitrate18.9 mg/L50 mg/L
38%
Hardness (as CaCO3)138 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%
Boron0.03 mg/L1 mg/L
3%
Cadmium0.0004 mg/L0.005 mg/L
8%
Chromium0.0025 mg/L0.05 mg/L
5%
Copper0.03 mg/L2 mg/L
2%
Iron0.01 mg/L0.2 mg/L
5%
Lead0.0012 mg/L0.01 mg/L
12%
Manganese0.0007 mg/L0.05 mg/L
1%
Mercury0.00007 mg/L0.001 mg/L
7%
Nickel0.0022 mg/L0.02 mg/L
11%
Selenium0.0004 mg/L0.04 mg/L
1%
Trihalomethanes0.04 mg/L0.1 mg/L
40%
Bromate0.001 mg/L0.01 mg/L
10%

138mg 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 Clasford Brook and Wood Street Brook, rated poor

The Environment Agency rated the Clasford Brook and Wood Street Brook 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 dissolved oxygen. 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

GU3 in short

Tap water in GU3 (Guildford) is supplied by Thames Water in the Guildford Central zone and scores 8.8 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 31 December 2025.

  • Nitrite is within its legal limit but flagged, at 76% of the 0.5 mg/L maximumAnything over three quarters of a limit is flagged here as worth watching. It has not gone over. See every reading
  • The lowest score of the 7 areas tested in GuildfordGU3 scores 8.8 out of 10. The best in Guildford, GU12, scores 9.4.
  • Moderately hard water at 138 mg/LSome scale over time in GU3, but not enough to justify a softener for most homes. How hardness is measured

Next door

KT249.4 out of 10 · 154 mg/LGU49.1 out of 10 · 75 mg/LGU129.4 out of 10 · 154 mg/LGU18.8 out of 10 · 204 mg/LGU29.4 out of 10 · 154 mg/LGU239.4 out of 10 · 154 mg/L

Questions about GU3 water

Is GU3 tap water safe to drink?

Based on the latest tests, GU3 (Guildford) water scores 8.8/10, which is safe. 1 of 23 tested contaminants exceeded recommended levels. Water is supplied by Thames Water.

What contaminants are in GU3 water?

We tested 23 contaminants in GU3 water. 1 were flagged, including Nitrite.

Who supplies water in GU3?

GU3 (Guildford) is supplied by Thames Water. You can view their full profile and compliance data on our supplier page.

Is GU3 water hard or soft?

Water in GU3 (Guildford) has a hardness of 138 mg/L CaCO3, which is classified as moderately hard. This is a moderate hardness level.

Should I use a water filter in GU3?

With 1 contaminant above recommended levels in GU3, 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 GU3 water?

No PFAS (forever chemicals) result is attached to the tap-water tests for GU3, 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 GU3?

The Environment Agency rated the Clasford Brook and Wood Street Brook 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 dissolved oxygen. 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 GU3, which is treated before it reaches homes.

Keep reading

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

River and groundwater readings near GU3

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
Iron0.7 mg/L0.2 mg/L
pH7.87 pHNone
Temperature13.7 °CNone
Conductivity693 µS/cmNone
Ammonia0.054 mg/L0.5 mg/L
Nitrate8.8 mg/L50 mg/L
Nitrite0.069 mg/L0.5 mg/L
Phosphate0.047 mg/LNone
Dissolved Oxygen7.63 mg/LNone

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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