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tapwater
England and Wales average 9.0

Tap water in GU18, Surrey HeathSafe to drink.Moderately soft.

Supplied by Thames Water. 74 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

9.3 / 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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Basic chlorine and taste improvement on a budget

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What's in a glass of GU18 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 38% of it. 18 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: 0.0006 mg/L, 1% of the 0.05 mg/L limitManganese1%Boron: 0.02 mg/L, 2% of the 1 mg/L limitBoron2%Copper: 0.04 mg/L, 2% of the 2 mg/L limitCopper2%Aluminium: 0.0082 mg/L, 4% of the 0.2 mg/L limitAluminium4%Iron: 0.009 mg/L, 5% of the 0.2 mg/L limitIron5%Chromium: 0.0025 mg/L, 5% of the 0.05 mg/L limitChromium5%Fluoride: 0.08 mg/L, 5% of the 1.5 mg/L limitFluoride5%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%Nickel: 0.0016 mg/L, 8% of the 0.02 mg/L limitNickel8%Lead: 0.0009 mg/L, 9% of the 0.01 mg/L limitLead9%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%Trihalomethanes: 0.015 mg/L, 15% of the 0.1 mg/L limitTrihalomethanes15%Nitrate: 9.4 mg/L, 19% of the 50 mg/L limitNitrate19%Nitrite: 0.19 mg/L, 38% of the 0.5 mg/L limitNitrite38%
  1. Nitrite38%
  2. Nitrate19%
  3. Trihalomethanes15%
  4. Bromate10%
  5. Lead9%
  6. Colour9%
  7. Cadmium8%
  8. Nickel8%
  9. Mercury7%
  10. Arsenic7%
  11. Antimony6%
  12. Fluoride5%
  13. Chromium5%
  14. Iron5%
  15. Aluminium4%
  16. Boron2%
  17. Copper2%
  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–
Fluoride0.08 mg/L1.5 mg/L
5%
Nitrate9.4 mg/L50 mg/L
19%
Nitrite0.19 mg/L0.5 mg/L
38%
Hardness (as CaCO3)88 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%
Copper0.04 mg/L2 mg/L
2%
Iron0.009 mg/L0.2 mg/L
5%
Lead0.0009 mg/L0.01 mg/L
9%
Manganese0.0006 mg/L0.05 mg/L
1%
Mercury0.00007 mg/L0.001 mg/L
7%
Nickel0.0016 mg/L0.02 mg/L
8%
Selenium0.0004 mg/L0.04 mg/L
1%
Trihalomethanes0.015 mg/L0.1 mg/L
15%
Bromate0.001 mg/L0.01 mg/L
10%

88mg of limescale minerals in every litre

Soft water. Kind to kettles, boilers and skin

You will not need a softener here, and you will use less soap and detergent than most of England.

Soft400 mg/L
Outside your tap

Your river is the Hale/Mill Bourne (Bagshot to Addlestone Bourne confluence near Chobham), rated moderate

The Environment Agency rated the Hale/Mill Bourne (Bagshot to Addlestone Bourne confluence near Chobham) 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 and fish. 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

GU18 in short

Tap water in GU18 (Surrey Heath) is supplied by Thames Water in the Surrey Heath Central zone and scores 9.3 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.

  • The cleanest tap water of the 6 areas tested in Surrey HeathGU18 scores 9.3 out of 10, ahead of GU16 in second place on 9.1.
  • Scores higher than all 5 neighbouring districtsThe nearest rival is GU16 on 9.1, against 9.3 here. Compare with GU16
  • Nothing tested came within 40% of its legal limitThe highest was Nitrite at 38% of the 0.5 mg/L maximum. See every reading

Next door

GU158.8 out of 10 · 138 mg/LGU169.1 out of 10 · 75 mg/LGU198.6 out of 10 · 225 mg/LGU207.8 out of 10 · 287 mg/LGU248.8 out of 10 · 138 mg/L

Questions about GU18 water

Is GU18 tap water safe to drink?

Based on the latest tests, GU18 (Surrey Heath) water scores 9.3/10, which is safe. 0 of 23 tested contaminants exceeded recommended levels. Water is supplied by Thames Water.

What contaminants are in GU18 water?

We tested 23 contaminants in GU18 water. None exceeded recommended safe levels.

Who supplies water in GU18?

GU18 (Surrey Heath) is supplied by Thames Water. You can view their full profile and compliance data on our supplier page.

Is GU18 water hard or soft?

Water in GU18 (Surrey Heath) has a hardness of 88 mg/L CaCO3, which is classified as moderately soft. This is a moderate hardness level.

Should I use a water filter in GU18?

GU18 water scored 9.3/10 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 GU18 water?

No PFAS (forever chemicals) result is attached to the tap-water tests for GU18, 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 GU18?

The Environment Agency rated the Hale/Mill Bourne (Bagshot to Addlestone Bourne confluence near Chobham) 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 and fish. 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 GU18, 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 GU18

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
pH7.52 pHNone
Temperature19.5 °CNone
Conductivity754 µS/cmNone
Nitrate12 mg/L50 mg/L
Nitrite0.029 mg/L0.5 mg/L
Phosphate0.55 mg/LNone
Iron0.11 mg/L0.2 mg/L
Dissolved Oxygen6.63 mg/LNone
Ammonia0.035 mg/L0.5 mg/L

Get alerts for your area

We'll email you when water quality data changes for GU18.

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