Built with researchers at Imperial College London
Scoring method
How the Home Water Health Score works
Every WaterGraph test ends in one number, the Home Water Health Score (the Water Health Score for short), and a verdict you can act on. The score runs from 0 to 100. Health readings make up half of it and wellness readings the other half, and any lead caps it.
Homes get a Home Water Health Score; areas get an Area Water Health Score once enough homes there have tested to cross our publication threshold.
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Nothing over UK health limits. However two readings need attention.
Three verdicts, set by your readings
The verdict at the top of your report comes from your readings, not your score. So a high score can still come with Attention. Very hard water, for example, has no UK health limit, but it's worth reviewing for wellness.
Every reading is in range.
Nothing over a UK health limit, but at least one reading needs attention.
Lead found, or a reading over a UK health limit.
For audit and technical review, every score also carries a grade (A 90 to 100, B 80 to 89, C 65 to 79, D 40 to 64, F 0 to 39) and the version of the method it was scored under.
The 8 readings we score
The same 8 readings as on What we test. Health readings make up half the score and wellness readings the other half.
Health readings
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Lead
UK limit 10 µg/L
Every test measures lead. No safe level is known, so any lead we can measure is flagged and caps your score.
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Nitrate
UK limit 50 mg/L
Nitrate comes mostly from farm fertiliser. The UK limit is set to protect bottle-fed babies. We flag it from 9 mg/L.
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Copper
UK limit 2 mg/L
Copper comes from copper pipes, most in water that has sat in them overnight. The UK limit is set to protect against stomach upset.
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Fluoride
UK limit 1.5 mg/L
Fluoride is added to some UK water at 1 mg/L to protect teeth, and occurs naturally in some groundwater. We flag it above 1.2 mg/L.
Wellness readings
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Iron
UK standard 0.2 mg/L
Iron comes mostly from old iron mains and pipes. We flag it from 0.1 mg/L, half the UK standard.
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pH
UK range 6.5 to 9.5
pH is how acidic or alkaline your water is. Below 6.5, water draws more lead and copper from pipes.
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Hardness
No UK limit
Hardness is how much calcium and magnesium your water carries. Hard water leaves limescale.
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Alkalinity
No UK limit
Alkalinity is your water's buffer, which keeps its pH steady.
The maths: weighted, normalised and capped
Each reading becomes a sub-score out of 100, and the sub-scores are combined by weight.
- Health readings, half of the score. Nitrate, copper and fluoride. Lead has no weight of its own: any lead caps the score instead.
- pH and iron, a third. Wellness readings.
- Hardness and alkalinity, a sixth. Wellness readings.
A reading with a UK limit scores 100 at zero, 60 at the limit and 0 at five times the limit. pH scores 100 near 8 and falls away outside 6.5 to 9.5. Hardness and alkalinity have no UK limit, so they score against typical UK levels. The exact weights within each group are available to academic reviewers on request.
Any lead caps the score at 40
If we find lead at any level, the score is capped at 40 and the verdict is Action Needed until a retest shows it's gone. Good readings elsewhere can't average lead away, so it sits outside the weighted score and is reported as measured. That's stricter than the UK limit of 10 µg/L and the EU's coming limit of 5 µg/L.
Independent recommendations
Every report comes with a Care Plan: a plain-English action list built from your results and your goals, with the exact next step for each. Readings that need attention come first, health readings before wellness ones, and free fixes come before products.
Our recommendations come from independent research, not commercial relationships.
- We don't sell water filters.
- We don't take payment to recommend products.
- No filter company or retailer has any say in your Care Plan.
Every recommendation is chosen on your readings, your goals and the evidence for what works.
What we measure against
Each result is checked against its UK limit, which matches the World Health Organization's guideline where it has one. The limits are set in UK law, in the Water Supply (Water Quality) Regulations 2016. Hardness and alkalinity have no UK limit, so the score compares them with typical UK levels.
The method is open to review. The calculation, the curves and the lead cap are on this page, and the weights are available to academic reviewers on request. Any score can be reproduced from its readings.
The method is versioned, and this is version 1.0. A score stays valid under the version it was worked out with. We don't re-score old results when the method changes.
A screening test, not a certificate
The Home Water Health Score shows where your home's water sits against UK limits and typical UK levels. It's a screening result, not a certificate that your water is safe, and not medical advice. Where a reading points to a possible compliance issue, we tell you plainly and always recommend an accredited lab test to confirm it.
Water score FAQs
What is a good water quality score?
Ours runs from 0 to 100, and 90 or more is grade A. The verdict matters more than the number: Clear means every reading is in range.
What happens to my score when I retest?
Each test gets its own score. If lead has gone, the cap lifts.
Test your tap
A lab test of your tap water, your Water Health Score and a Care Plan, posted UK-wide. From £49.