Bacteria and E. coli in drinking water: what a positive means, and what to do
On mains water, bacteria problems are rare: the DWI says “It is extremely rare for drinking water to cause illness in England and Wales.” The risk is higher on private supplies, storage tanks and after flooding. E. coli is the one that matters most, because in one council’s words it is “present in human and animal faeces”. If a test finds it, stop drinking the water untreated and tell your water company or council.
DWINorth Norfolk DC Last checked 28 Sep 2026 Get the E. coli Test · £15.95- Quotes from UK regulators, linked
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13 tests £55 £45 View kit What a home screen doesn't cover: enterococci and colony counts need a lab. Your council or water company can arrange testing.Is this you?
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COMMON After heavy rain or flooding Rain can wash bacteria into a source. Retest for E. coli. E. coli Test → Well, borehole or spring Private supplies need regular testing. Build a plan for yours. Private supplies guide →Bacteria Next Steps
What should you do now?
Four quick taps: where your water comes from, what has happened, who drinks it, and whether there is a boil notice. You get what to do today, who to tell, and the test that fits.
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What E. coli and coliforms tell you
Home and council tests look for bacteria that signal contamination. The legal standard for E. coli is zero: the DWI's standards table lists E. coli at 0 per 100 ml, measured at the consumer's tap DWI.
Coliform bacteria“Coliform bacteria are found widely in the environment.” North Norfolk DC “Their presence indicates that the water supply has had some form of general environmental contamination, such as surface run off into a well, dust in a storage tank, or dirt inside a tap.” North Norfolk DCE. coli and enterococci“E. coli and Enterococci are present in human and animal faeces and are pathogens.” North Norfolk DC “Their presence also indicates that other harmful pathogens could be in the water.” North Norfolk DCNot every E. coli makes people ill, but you can't tell which kind is in your water from a screen. NHS inform says “Most types of E. coli are harmless and are an important part of a healthy digestive tract. However, some can make you unwell.” NHS inform One group, STEC, “can cause severe stomach pain, bloody diarrhoea and kidney failure.” NHS inform
“E. coli and Enterococci are present in human and animal faeces and are pathogens. This means that they can make people ill.”North Norfolk District Council North Norfolk DC
Where bacteria get in
Bacteria get in where water meets the outside world. Tap a number on the diagram at the top of the page, or read the four points below.
1 The source, after rain The DWI says “Wells and springs although derived from groundwater, are very often influenced by surface water, and are considered surface water for the purposes of water quality risks.” DWI Retest after heavy rain. 2 Treatment A UV lamp is “Very effective if maintained correctly.” North Norfolk DC But it “Can stop working and not be noticed if not checked or alarmed.” North Norfolk DC Retest after lamp or filter work. 3 Storage tanks A tank needs a lid that “excludes light and is tightly fitting and securely fastened, so that birds, vermin, and dust cannot get into the water.” DWI Check the lid and screens. 4 The tap Coliforms can come from “dirt inside a tap” North Norfolk DC, which is why a careful sample matters. Clean the tap before sampling.Rain is the big one for private supplies. Food Standards Scotland notes that “heavy rainfall can significantly deteriorate the microbiological quality of various water sources” FSS.
After heavy rain or flooding? A single E. coli test is the quick retest. E. coli Test · £15.95Mains water or a private supply
On mains water, bacteria problems are rare. The DWI says “It is extremely rare for drinking water to cause illness in England and Wales.” DWI and “Tap water in the UK is safe to drink without boiling.” DWI
When something does go wrong, it is usually local: a tank, a tap or the pipes in the building. The DWI explains that in older homes “this storage tank will provide cold water to upstairs bathrooms but in some properties all of the cold-water taps may be fed from this tank.” DWI
Private supplies are different: nobody treats or tests the water for you unless you ask. If E. coli is confirmed, “If E. coli and/or Enterococci have been found a Notice is likely to be served by the council.” North Norfolk DC
The private water supplies guide →If a test is positive
If bacteria are found What to do today- 1. Stop drinking it untreated. Under a boil water notice, the DWI's advice is to “boil it before you drink it, use it to brush your teeth, make ice cubes, prepare food, clean feeding equipment or give it to your pets” DWI. Or use bottled water.
- 2. Tell the right people. Mains water: your water company. “Your water company may come to your property and take some water quality samples.” DWI Private supply: your council's environmental health team.
- 3. Confirm, find the cause, retest. A home screen is not a lab result. Confirm it, check the source, treatment, tank and tap (chapter 02), then retest before drinking untreated.
Coliforms without E. coli are treated differently. One council explains that “If only coliform bacteria and/or high colony counts have been confirmed the council will not normally serve a notice or visit to investigate or re-sample” North Norfolk DC, but it still recommends the same short-term steps. Its options include “Collect mains water from friends or family. Use clean sealable containers and store in the fridge.” North Norfolk DC
Read my resultBoiling water safely
Boiling works on germs. The DWI says “Heating water is one of the best ways to kill or inactivate bacteria, viruses or parasites.” DWI “Boiling water is also effective against parasites such as Cryptosporidium.” DWI
The DWI's method
“You should boil your water until it reaches a rolling ball.” DWI
“Remove the water from the heat and allow it to cool naturally.” DWI “The water should be stored in a clean container, in the fridge and should be discarded if not used within 24 hours.” DWI
For washing, “The water is still safe to shower and bathe in, but make sure it does not get into your mouth.” DWI Making up baby formula? The NHS advice is to “leave the water to cool for no more than 30 minutes, so that it remains at a temperature of at least 70C” NHS.
Illness and getting help
If you think the water has made someone ill, the DWI's advice is clear: “If you believe that your drinking water is causing illness, you should consult a doctor and contact your water company in the first instance.” DWI On a private supply, tell your council too.
NHS inform lists ways people catch STEC, including “drinking contaminated water from inadequately treated water supplies” NHS inform and “drinking contaminated water from streams, rivers and lakes” NHS inform. It says to contact your GP practice urgently if “you or your child has bloody diarrhoea” NHS inform, and “Phone 111 if your GP practice is closed.” NHS inform
This page is not medical advice. If you are worried about someone's health, speak to a doctor or call 111.
07 Taking a good sample
A bacteria screen is only as good as the sample. Coliforms can come from “dirt inside a tap” North Norfolk DC, so a dirty tap or a touched cap can give a positive that isn't in your water.
- Follow the kit's instructions exactly, and use the cold kitchen tap unless they say otherwise.
- Take off any filter, hose or anti-splash fitting, and clean the tap outlet first.
- Don't touch the inside of the sample pot or its lid.
- Write down the date, the tap and anything recent: rain, work on the supply, a new tank.
Our E. coli Test screens one sample for E. coli and coliform bacteria. It is a screen, not an accredited lab test, so confirm a positive before making big decisions.
Got a result? Decode it in the Result Centre →08 Fixing the cause
On a private supply, the fix is usually at the source, the treatment or the tank. For a shallow source, one council says “It is often difficult to prove and stop this type of contamination. Treatment or changing to a deep borehole or mains water is normally the best long term solution.” North Norfolk DC
UV lamp“UV light inactivates the bacteria.” North Norfolk DC It “Needs clear water (low turbidity and colour) to be effective.” North Norfolk DCChlorination“Provides residual disinfection properties.” North Norfolk DC But “Dosing chemicals need careful storage and handling.” North Norfolk DCTanks“Cleaning and disinfecting existing tank. Ensuring close-fitting lid and gauze on overflow to exclude insects.” North Norfolk DCWell heads“Surround the top of a Well with a raised chamber with a sealed and locked cover.” North Norfolk DCWe don't sell treatment systems, so this is an overview, not a recommendation. After any fix, retest for E. coli before drinking the water untreated.
Treatment options in the private supplies guide →09 Storage tanks and bathroom taps
Many older homes store cold water in the loft. The DWI's view: “Ideally you should only use a tap connected to the mains water supply for drinking, food preparation or teeth cleaning” DWI.
Not sure which taps are on the tank? “If you are able to, hold back all the water with your thumb when the tap is fully open, then the tap is likely to be connected to a tank not the mains.” DWI
The DWI DWI says water in a tank will deteriorate if:
- “There is no lid on the storage tank”
- “The water becomes warm”
- “Too much water is stored and turnover is low”
Renting? “If you are renting your property privately then your landlord is responsible for these checks.” DWI
Why to drink from the kitchen tap →Near you
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Bacteria and E. coli questions
Short answers, with the regulator's own words where it matters.
What does E. coli in drinking water mean?
That faecal matter has got into the water somewhere. “E. coli and Enterococci are present in human and animal faeces and are pathogens.” North Norfolk DC The legal standard at the tap is zero.
Are coliform bacteria dangerous?
On their own they are a warning sign rather than proof of danger. “Coliform bacteria are found widely in the environment.” North Norfolk DC They point to contamination, such as run-off, a dusty tank or a dirty tap, so find and fix the cause.
Is UK tap water safe from bacteria?
Mains water is disinfected and tested. The DWI says “It is extremely rare for drinking water to cause illness in England and Wales.” DWI Private supplies, tanks and taps are where problems usually start.
Does boiling water kill E. coli?
Yes. The DWI says boiling means “any bacteria or viruses that were in your water are killed or deactivated” DWI. Bring it to a rolling boil, then let it cool.
Can I shower if E. coli is found?
Under a boil notice, “The water is still safe to shower and bathe in, but make sure it does not get into your mouth.” DWI
How often should a well or borehole be tested for bacteria?
We suggest at least once a year, plus a retest after heavy rain, flooding or any work on the supply. The Private Supply Planner builds a plan for your supply.
Open the Private Supply Planner →Can a home test detect E. coli?
Yes, as a first screen. Our E. coli Test screens one sample for E. coli and coliform bacteria. It is not an accredited lab result, so confirm a positive with your council, water company or a lab.
Who do I tell about a positive result?
Mains water: your water company. “Your water company may come to your property and take some water quality samples.” DWI Private supply: your council's environmental health team.
Keep reading
E. coli or coliforms in your water test? What to do next What is the level of E. coli in UK water? Is borehole, well or spring water safe to drink? Borehole water treatment and private supply maintenanceSources and how we write these pages · 9 sources · last checked 28 Sep 2026
- DWI: Drinking water standards and regulations checked 28 Sep 2026
- DWI: Receiving a boil water notice checked 28 Sep 2026
- DWI: Illness checked 28 Sep 2026
- DWI: Water storage tanks and cisterns checked 28 Sep 2026
- DWI: Protecting your private water supply checked 28 Sep 2026
- North Norfolk District Council: Microbiological failure checked 28 Sep 2026
- NHS inform: Shiga toxin-producing E. coli (STEC) checked 28 Sep 2026
- NHS: Making up baby formula checked 28 Sep 2026
- Food Standards Scotland: Water sources and storage 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.
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