Understand your water test result: what it means, and what to do next
Compare your number with the UK standard, in the same units, for water from the cold kitchen tap. The DWI says “The standards are strict and include wide safety margins.” Most apply at the tap: E. coli 0, lead 10 µg/l, arsenic 10 µg/l, fluoride 1.5 mg/l. The Result Decoder below tells you what your result means and the next step.
DWI Last checked 28 Sep 2026 Get the Complete Kit · £45- The DWI’s standards, linked
- Home screens and lab reports
- Clear next steps for each result
Result Decoder
What does your result mean?
Tick every test you did (one or several), say what each showed and where the sample came from. You get what each result means against the UK standard, and one clear list of what to do next.
Your answers stay in your browser.
Is this you?
Start from your result
Pick the card that matches your result. Each one takes you to the right part of this page or the right guide.
Share it with your area Add your result to the UK testing map. Add my result →How to read any water result
Four things turn a number into an answer: the units, the standard, where the sample came from, and what kind of test it was. Tap a number on the diagram at the top of the page, or read the four points below.
1 The units The DWI's key: “µg/L Micrograms per litre (parts per billion)” and “mg/L: Milligrams per litre (parts per million)” DWI. So 10 ppb is 10 µg/l, and 1 ppm is 1 mg/l. 1 mg/l = 1,000 µg/l. 2 The standard Each substance has a maximum. “The standards are strict and include wide safety margins.” DWI Compare like with like. 3 Where it was taken The point of compliance is “The point where the legal standards apply, normally this is the consumers tap but it may be at the water works.” DWI Test the cold kitchen tap. 4 Home screen or lab A home screen is a result for that sample at that time. It is not accredited lab confirmation, so confirm anything unexpected. Screen first, confirm if high.“Drinking water must be ‘wholesome’ and this is defined in law mainly by setting standards for a wide range of substances, organisms and properties of water in regulations.”Drinking Water Inspectorate DWI
The UK standards at a glance
These are the legal standards in England and Wales for the things people most often test, from the DWI's published tables DWI. Most apply at the consumer's tap.
What Standard Home screen Guide E. coli Standard: 0 per 100 ml Home screen: Yes · E. coli Test Guide: Bacteria guide Enterococci Standard: 0 per 100 ml Home screen: Not available Guide: Lab only Lead Standard: 10 µg/l Home screen: Yes · Lead Test Guide: Lead guide Arsenic Standard: 10 µg/l Home screen: Yes · Arsenic Test Guide: Arsenic guide Fluoride Standard: 1.5 mg/l Home screen: Yes · Fluoride Test Guide: Fluoride guide Nitrate Standard: 50 mg/l Home screen: Not available Guide: Lab only Copper Standard: 2.0 mg/l Home screen: Not available Guide: Lab only Iron Standard: 200 µg/l Home screen: Not available Guide: Taste and colour guide Manganese Standard: 50 µg/l Home screen: Not available Guide: Taste and colour guide Sodium Standard: 200 mg/l Home screen: Not available Guide: Lab only Chlorine Standard: Not in the standards table Home screen: Yes · Chlorine Test Guide: Chlorine guideTaste and odour have a standard too, in words rather than numbers: “Acceptable to consumers and no abnormal change” DWI.
Bacteria results
Bacteria results are usually present or absent, and the standard for E. coli is zero. What each finding means, in one council's words:
Coliforms only“Coliform bacteria are found widely in the environment.” North Norfolk DC They point to contamination somewhere, such as “dirt inside a tap” North Norfolk DC. E. coli“E. coli and Enterococci are present in human and animal faeces and are pathogens.” North Norfolk DC Stop drinking the water untreated. A positive bacteria result? What to do today, who to tell, and how to boil water safely. Bacteria guideLead and arsenic results
Lead and arsenic share the same standard: 10 micrograms per litre at the tap DWI. A result below that meets the standard for that sample; a result at or above it needs confirming and acting on.
LeadUsually from old pipes or fittings, so a high result points to plumbing. The DWI's short-term advice: “For drinking and cooking, run the tap to clear any water that has been standing in the pipework for while, for example, overnight.” DWILead guide →ArsenicUsually from the ground, so a high result points to the source. “If a water sample fails for arsenic it would be prudent to gather additional samples to verify the failure and determine the variability of the concentration of arsenic in water.” DWQRArsenic guide →Chlorine and fluoride results
ChlorineThere is no UK maximum in the standards table. “Typically, water companies keep the level of residual disinfectant in the form of free or combined chlorine to 0.5 mg/l or less.” DWIChlorine guide →Fluoride“The maximum permitted value of fluoride in drinking water is 1.5mg/l (milligrams per litre).” DWI Fluoridated areas dose to about 1 mg/l. Fluoride guide →Home screen, water company, council or lab
Each route answers a different question.
A home screenQuick, and done on your terms. It is a result for the sample tested at that time. It does not prove future safety, replace an official investigation, or give accredited lab confirmation. Your water companyFor mains water, they can investigate at your tap. “Your water company may come to your property and take some water quality samples.” DWIYour councilFor private supplies in England and Wales, the council is the regulator and can test on request, for a fee. An accredited labAn exact figure for a wide range of substances. The route to confirm a high home result.07 Add your result to the map
Adding your result to the UK testing map helps your neighbours see what people are finding in your area. Results are checked before they appear on the map, and the map shows community results alongside public data. It is not official monitoring.
Add my resultOpen the UK testing map08 When to retest
One result is a snapshot. Our suggestions for when to test again:
- After a positive or high result: after the fix, before relying on the water again.
- Private supplies: once a year in the same month, and after heavy rain or work on the supply.
- After plumbing work, new taps or a new tank.
- When the taste, smell or colour changes.
Retest or confirm
Kits for a retest
All water tests Retest everythingComplete Drinking Water Test Kit
Choose this for a full retest after a fix, or a first look at everything.
1 × E. coli 1 × lead 1 × arsenic 5 × chlorine 5 × fluorideE. coli, lead and arsenic, plus chlorine and fluoride.
£55 £45 View kitE. coli Test
The quick retest after a bacteria result, once you have fixed the cause.
E. coli £15.95 View kitLead, E. coli and Arsenic Test Kit
E. coli, lead and arsenic: the three safety checks together.
E. coli · lead · arsenic £35 View kit A home screen is not a lab result. To confirm a high or positive result, use your water company, your council or an accredited lab.Near you
Check your postcode
See your water company and hardness, then compare your result with community results near you on the UK testing map.
Open the UK testing mapAdd my resultThe map shows community results and public data. It is not official monitoring. Area facts are taken at the centre of your postcode district.
Community results Housing ageQuestions people ask
Water result questions
Short answers, with the regulator's own words where it matters.
What does ppb mean on a water test?
Parts per billion. It is the same as micrograms per litre: the DWI's key reads “µg/L Micrograms per litre (parts per billion)” DWI. Lead and arsenic standards are both 10 ppb.
What does 0 per 100 ml mean?
It is the standard for E. coli and enterococci: none should be found in a 100 ml sample. Any detection fails the standard.
My home test is positive. What now?
Use the Result Decoder on this page, and tick every test you did. For bacteria, stop drinking the water untreated and tell your water company or council. For lead or arsenic, confirm the result and follow the steps in that guide.
Is a home test as accurate as a lab?
No. A home screen is a quick first check of one sample. A lab gives an exact, accredited figure. Use a home screen to decide whether you need a lab test.
My result is just under the standard. Is that OK?
It meets the standard for that sample. Levels can change, especially lead with standing water, so we suggest a retest. “The standards are strict and include wide safety margins.” DWI
What are the UK limits for lead, arsenic and fluoride?
Lead 10 µg/l, arsenic 10 µg/l and fluoride 1.5 mg/l, from the DWI's standards tables DWI.
How do I add my result to the map?
Use the test result form. Results are checked before they appear.
Add my result →Who can test my water properly?
Mains water: your water company. Private supply: your council, or an accredited lab.
Keep reading
E. coli or coliforms in your water test? What to do next How to test water quality at home, step by step Is UK tap water safe to drink? The 2026 evidence What is the level of lead in UK water?Sources and how we write these pages · 7 sources · last checked 28 Sep 2026
- DWI: Drinking water standards and regulations checked 28 Sep 2026
- DWI: Lead in drinking water checked 28 Sep 2026
- DWI: Chlorine checked 28 Sep 2026
- DWI: Fluoridation of drinking water checked 28 Sep 2026
- DWI: Illness checked 28 Sep 2026
- DWQR: Arsenic checked 28 Sep 2026
- North Norfolk District Council: Microbiological failure checked 28 Sep 2026
How we write these pages. Health and safety lines are quoted word for word from the source and linked, with the date we last checked them. Home screening is a first check, not lab certification. Last reviewed 28 Sep 2026.
Where to next?
Your next step, whatever your result
Retest everything Complete Drinking Water Test Kit13 tests · E. coli, lead and arsenic, plus chlorine and fluoride
£55 £45 View kit Not sure which test? Decode your resultWhat you tested, what it showed, where it came from, who drinks it.
Which test do I need? Your area What we know near you Open the map Area facts come from the same public data as the UK testing map. Already tested? Share your resultAdd it to the UK testing map so neighbours can see what people are finding in your area.
Open the mapAdd my result Related guides Other water concerns Private water suppliesLeadBacteria and E. coliArsenicTaste and smellFluoride Stay informed Results alerts for your areaBe told when a new community result is added in your area. Sign up on the UK testing map.
Get area alerts- ✓ Quotes from UK regulators, linked and dated
- ✓ Home screens, not lab certificates
- ✓ Shop links open in a new tab, so this guide stays open