MARLBOROUGH: your water explained
Published results for this named supply area. Your address may be served by a different area.
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Your water at a glance
Very hard water. Expect limescale.
For your home, the main practical issue is mineral scale in kettles, showers and appliances. Check your dishwasher setting and follow appliance care instructions.
302 mg/l as CaCO₃
Soft ≤100 · Slightly hard ≤150 · Moderately hard ≤200 · Hard ≤300 · Very hard >300 mg/l. DWI hardness bands; not safety grades.
Published quality checks
More context is needed
These labels describe 2024. 22 other parameters have no complete compliance judgement here. They are not a guarantee about an individual tap today.
Understand the reported results ↓Make this useful for your home
Hardness reporting period: 2024 · Quality reporting period: 2024
Appliance settings · Convert hardness units
3.02 mmol/l
A conversion of the published hardness, not another test. Follow your appliance’s model-specific instructions.
A newer source document is awaiting validation. The figures here remain from the approved period shown. Original supplier report ↗
Drinking-water results
What do the important results mean?
Read the status, sample range and source requirement together. A low average can hide an individual exceedance. Green labels mean the supplier reported no exceedances for that parameter and period; amber calls for source context.
Lead
No numerical limit supplied
Published mean
1.2 µg/l
Source reference: Not supplied
Plumbing can affect lead at an individual tap. An area average cannot rule out a problem with pipes at your property.
8 samples · Range: <0.9 to 2.1 µg/l
This report gives no numerical limit for this parameter. A higher or lower number is not automatically better.
Nitrate
No numerical limit supplied
Published mean
41 mg/l
Source reference: Not supplied
A dissolved compound monitored against drinking-water requirements. Its mean, highest reported result and sample count answer different questions.
8 samples · Range: 37 to 45 mg/l
This report gives no numerical limit for this parameter. A higher or lower number is not automatically better.
Fluoride
No numerical limit supplied
Published mean
0.07 mg/l
Source reference: Not supplied
Can occur naturally or be added through a fluoridation scheme. The concentration alone does not tell you whether it was added; a lower number is not automatically better.
8 samples · Range: 0.07 to 0.1 mg/l
This report gives no numerical limit for this parameter. A higher or lower number is not automatically better.
For your household
What should you do next?
Check appliance settings
Match the hardness unit to your dishwasher manual. Settings depend on the model.
Dishwasher guideManage limescale
Follow the manufacturer’s descaling advice. Check what a filter actually removes before buying.
Filters and limescaleA new change at your tap?
For a new taste, smell, colour or supply problem, check current supplier advice. Annual data is not a live incident feed.
Official supplier help ↗Taste, appearance and mineral content
Chlorine, pH and minerals answer different questions. Calcium and magnesium help describe hardness; chloride is different from treatment chlorine. None is a stand-alone water-quality score.
Chlorine residual
Disinfectant remaining after treatment. It can influence taste and smell; a lower concentration is not automatically better.
See the measurement and context ↓pH
Describes acidity and alkalinity on a scale, rather than an amount of a substance. Where the source gives a range, both its lower and upper bounds matter.
See the measurement and context ↓Has the hardness changed?
History for this reported source area. Only comparable annual statistics appear in the chart; rolling summaries are kept separate. These are not daily tests at your address.
A comparable historical series is not available yet. We will add earlier reports when we can verify their periods and source areas.
Explore all measurements · 24 parameters · 2024
Every result retains its original units, range, sample count and source notes. Comparisons use the reference printed in this report; qualitative references and missing limits are not converted into invented pass/fail judgements. Unlisted substances are not necessarily absent from the water.
Parameters without their own explanation: A substance monitored in this supplier report. The source reference, units, sample range and any reported failures provide its context; the number alone is not a water-quality rating.
Hardness and minerals 7 parameters
Total hardness
No numerical limit supplied
Published mean
302 mg/l as CaCO₃
Source reference: Not supplied
Dissolved calcium and magnesium affect limescale and appliance settings. This is a mineral description, not a safety score.
4 samples · Range: 295 to 311 mg/l as CaCO₃
This report gives no numerical limit for this parameter. A higher or lower number is not automatically better.
Original wording and source notes
Source reference: Not supplied. Source parameter: Hardness (Total) as CaCO3. Original mean: 302 mg/l as CaCO₃.
Fluoride
No numerical limit supplied
Published mean
0.07 mg/l
Source reference: Not supplied
Can occur naturally or be added through a fluoridation scheme. The concentration alone does not tell you whether it was added; a lower number is not automatically better.
8 samples · Range: 0.07 to 0.1 mg/l
This report gives no numerical limit for this parameter. A higher or lower number is not automatically better.
Original wording and source notes
Source reference: Not supplied. Source parameter: Fluoride as F. Original mean: 0.07 mg/l.
Magnesium
No numerical limit supplied
Published mean
1.5 mg/l
Source reference: Not supplied
A naturally occurring mineral that contributes to hardness alongside calcium.
4 samples · Range: 1.4 to 1.5 mg/l
This report gives no numerical limit for this parameter. A higher or lower number is not automatically better.
Original wording and source notes
Source reference: Not supplied. Source parameter: Magnesium. Original mean: 1.5 mg/l.
Alkalinity
No numerical limit supplied
Published mean
252 mg/l as CaCO₃
Source reference: Not supplied
How strongly water resists a change in acidity. This helps describe its chemistry; it is different from pH and total hardness.
4 samples · Range: 244 to 259 mg/l as CaCO₃
This report gives no numerical limit for this parameter. A higher or lower number is not automatically better.
Original wording and source notes
Source reference: Not supplied. Source parameter: Alkalinity as CaCO3. Original mean: 252 mg/l as CaCO₃.
Sodium
No numerical limit supplied
Published mean
6 mg/l
Source reference: Not supplied
A dissolved salt component. Compare the water measurement with its source reference; it is not a measure of your total dietary salt intake.
9 samples · Range: 6 to 7 mg/l
This report gives no numerical limit for this parameter. A higher or lower number is not automatically better.
Original wording and source notes
Source reference: Not supplied. Source parameter: Sodium as Na. Original mean: 6 mg/l.
Chloride
No numerical limit supplied
Published mean
17 mg/l
Source reference: Not supplied
A dissolved salt component that can influence taste at higher concentrations. It is different from chlorine used in treatment.
8 samples · Range: 16 to 17 mg/l
This report gives no numerical limit for this parameter. A higher or lower number is not automatically better.
Original wording and source notes
Source reference: Not supplied. Source parameter: Chloride as Cl. Original mean: 17 mg/l.
Sulphate
No numerical limit supplied
Published mean
12 mg/l
Source reference: Not supplied
A dissolved mineral component monitored in water-quality reports. Read its concentration alongside the source reference.
8 samples · Range: 10 to 14 mg/l
This report gives no numerical limit for this parameter. A higher or lower number is not automatically better.
Original wording and source notes
Source reference: Not supplied. Source parameter: Sulphate as SO4. Original mean: 12 mg/l.
Taste, appearance and treatment 5 parameters
pH
No numerical limit supplied
Published mean
7.3 pH units
Source reference: Not supplied
Describes acidity and alkalinity on a scale, rather than an amount of a substance. Where the source gives a range, both its lower and upper bounds matter.
12 samples · Range: 7.2 to 7.4 pH units
This report gives no numerical limit for this parameter. A higher or lower number is not automatically better.
Original wording and source notes
Source reference: Not supplied. Source parameter: Hydrogen Ion. Original mean: 7.3 pH units.
Chlorine residual
No numerical limit supplied
Published mean
0.59 mg/l
Source reference: Not supplied
Disinfectant remaining after treatment. It can influence taste and smell; a lower concentration is not automatically better.
25 samples · Range: 0.48 to 0.7 mg/l
This report gives no numerical limit for this parameter. A higher or lower number is not automatically better.
Original wording and source notes
Source reference: Not supplied. Source parameter: Chlorine (Residual). Original mean: 0.59 mg/l.
Colour
No numerical limit supplied
Published mean
<1.8 mg/l Pt/Co
Source reference: Not supplied
A measure of water colour under test conditions. A new change at your tap should be checked with your supplier.
12 samples · Range: <1.8 to <1.8 mg/l Pt/Co
This report gives no numerical limit for this parameter. A higher or lower number is not automatically better.
“<” is part of the source result. It is not an exact concentration or a measured zero.
Original wording and source notes
Source reference: Not supplied. Source parameter: Colour. Original mean: <1.8 mg/l Pt/Co.
Turbidity
No numerical limit supplied
Published mean
<0.09 FTU
Source reference: Not supplied
Measures cloudiness caused by suspended particles. It cannot identify their cause on its own.
12 samples · Range: <0.09 to <0.09 FTU
This report gives no numerical limit for this parameter. A higher or lower number is not automatically better.
“<” is part of the source result. It is not an exact concentration or a measured zero.
Original wording and source notes
Source reference: Not supplied. Source parameter: Turbidity. Original mean: <0.09 FTU.
Conductivity
No numerical limit supplied
Published mean
531 µS/cm
Source reference: Not supplied
Indicates how readily water conducts electricity, influenced by dissolved ions. It is not a direct measurement of hardness or safety.
12 samples · Range: 511 to 554 µS/cm
This report gives no numerical limit for this parameter. A higher or lower number is not automatically better.
Original wording and source notes
Source reference: Not supplied. Source parameter: Conductivity. Original mean: 531 µS/cm.
Metals 8 parameters
Lead
No numerical limit supplied
Published mean
1.2 µg/l
Source reference: Not supplied
Plumbing can affect lead at an individual tap. An area average cannot rule out a problem with pipes at your property.
8 samples · Range: <0.9 to 2.1 µg/l
This report gives no numerical limit for this parameter. A higher or lower number is not automatically better.
Original wording and source notes
Source reference: Not supplied. Source parameter: Lead as Pb. Original mean: 1.2 µg/l.
Iron
No numerical limit supplied
Published mean
5 µg/l
Source reference: Not supplied
Can affect water colour, staining and taste. A historical result does not diagnose a change in your tap water today.
9 samples · Range: <5 to 5 µg/l
This report gives no numerical limit for this parameter. A higher or lower number is not automatically better.
Original wording and source notes
Source reference: Not supplied. Source parameter: Iron as Fe. Original mean: 5 µg/l.
Aluminium
No numerical limit supplied
Published mean
<8.2 µg/l
Source reference: Not supplied
Monitored as part of water-quality testing and treatment control. Compare with the reference and sample results in the source.
9 samples · Range: <8.2 to <8.2 µg/l
This report gives no numerical limit for this parameter. A higher or lower number is not automatically better.
“<” is part of the source result. It is not an exact concentration or a measured zero.
Original wording and source notes
Source reference: Not supplied. Source parameter: Aluminium as Al. Original mean: <8.2 µg/l.
Copper
No numerical limit supplied
Published mean
0.146 mg/l
Source reference: Not supplied
Can be influenced by plumbing. The area report does not replace investigation of a problem at an individual property.
8 samples · Range: 0.027 to 0.39 mg/l
This report gives no numerical limit for this parameter. A higher or lower number is not automatically better.
Original wording and source notes
Source reference: Not supplied. Source parameter: Copper as Cu. Original mean: 0.146 mg/l.
Manganese
No numerical limit supplied
Published mean
<0.5 µg/l
Source reference: Not supplied
Can affect colour and deposits. Any reported exceedance needs the supplier’s investigation context.
9 samples · Range: <0.5 to <0.5 µg/l
This report gives no numerical limit for this parameter. A higher or lower number is not automatically better.
“<” is part of the source result. It is not an exact concentration or a measured zero.
Original wording and source notes
Source reference: Not supplied. Source parameter: Manganese as Mn. Original mean: <0.5 µg/l.
Nickel
No numerical limit supplied
Published mean
3.4 µg/l
Source reference: Not supplied
A monitored metal that can be influenced by materials in contact with water. Local plumbing and sampling context matter.
8 samples · Range: <0.7 to 22.4 µg/l
This report gives no numerical limit for this parameter. A higher or lower number is not automatically better.
Original wording and source notes
Source reference: Not supplied. Source parameter: Nickel as Ni. Original mean: 3.4 µg/l.
Arsenic
No numerical limit supplied
Published mean
<0.7 µg/l
Source reference: Not supplied
A trace element monitored against a drinking-water requirement. Use the source results and units rather than taste or appearance to interpret it.
8 samples · Range: <0.7 to <0.7 µg/l
This report gives no numerical limit for this parameter. A higher or lower number is not automatically better.
“<” is part of the source result. It is not an exact concentration or a measured zero.
Original wording and source notes
Source reference: Not supplied. Source parameter: Arsenic as As. Original mean: <0.7 µg/l.
Selenium
No numerical limit supplied
Published mean
0.4 µg/l
Source reference: Not supplied
A trace element monitored in drinking water. Its presence alone does not establish that a requirement was exceeded.
8 samples · Range: 0.4 to 0.5 µg/l
This report gives no numerical limit for this parameter. A higher or lower number is not automatically better.
Original wording and source notes
Source reference: Not supplied. Source parameter: Selenium as Se. Original mean: 0.4 µg/l.
Other monitored substances 4 parameters
Nitrate
No numerical limit supplied
Published mean
41 mg/l
Source reference: Not supplied
A dissolved compound monitored against drinking-water requirements. Its mean, highest reported result and sample count answer different questions.
8 samples · Range: 37 to 45 mg/l
This report gives no numerical limit for this parameter. A higher or lower number is not automatically better.
Original wording and source notes
Source reference: Not supplied. Source parameter: Nitrate as NO3. Original mean: 41 mg/l.
Trihalomethanes
No numerical limit supplied
Published mean
3 µg/l
Source reference: Not supplied
About this parameter: see the note above this list.
8 samples · Range: 2 to 4 µg/l
This report gives no numerical limit for this parameter. A higher or lower number is not automatically better.
Original wording and source notes
Source reference: Not supplied. Source parameter: Trihalomethanes. Original mean: 3 µg/l.
Bromate
No numerical limit supplied
Published mean
<0.5 µg/l
Source reference: Not supplied
About this parameter: see the note above this list.
8 samples · Range: <0.5 to <0.5 µg/l
This report gives no numerical limit for this parameter. A higher or lower number is not automatically better.
“<” is part of the source result. It is not an exact concentration or a measured zero.
Original wording and source notes
Source reference: Not supplied. Source parameter: Bromate. Original mean: <0.5 µg/l.
Ammonium as NH4
No numerical limit supplied
Published mean
<0.03 mg/l
Source reference: Not supplied
About this parameter: see the note above this list.
8 samples · Range: <0.03 to <0.03 mg/l
This report gives no numerical limit for this parameter. A higher or lower number is not automatically better.
“<” is part of the source result. It is not an exact concentration or a measured zero.
Original wording and source notes
Source reference: Not supplied. Source parameter: Ammonium as NH4. Original mean: <0.03 mg/l.
Sources, dates and how to interpret this page
- Reporting period
- 2024
- Source retrieved
- 2026-02-27
- Last verified source check
- 2026-09-20
- Original publication
- Thames Water report ↗
Published area statistics are not a test at your home or a current incident report.
Hardness: 4 samples · reported range 295 to 311 mg/l as CaCO₃.
Status labels describe the published parameter and period. Historical exceedances do not automatically establish a current incident. Numerical limits are taken from the original report, not applied indiscriminately across countries, dates or sampling locations. DWI explains how standards work in England and Wales.
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Town pages for this source area
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