Boil water notices
What triggers one, what to do, how long boiling needs, and the situations where boiling makes the problem worse rather than better.
What triggers one
- Loss of pressure in the distribution network, which can draw contaminated water in through defects — this is the most common trigger, and the notice is precautionary
- A burst main, or repair work that opened the network
- Detection of E. coli or coliforms in the supply
- Flooding of a source or a treatment works
- A treatment failure, such as a disinfection or filtration problem
Most boil water notices are precautionary. They are issued because a risk of contamination arose, not because contamination was confirmed — and issuing one quickly is far better practice than waiting for a microbiological result that takes a day to come back.
How long to boil
| Use | Guidance |
|---|---|
| Drinking | Boil first, or use bottled water |
| Making tea, coffee, squash | Boil first |
| Preparing food, washing salad | Boil first |
| Making up infant formula | Boil first. This matters most of all |
| Brushing teeth | Boil first |
| Ice | Do not use ice made before the notice; discard it |
| Washing hands | Tap water with soap is generally fine unless told otherwise |
| Showering and bathing | Generally fine for adults; avoid swallowing. Supervise young children |
| Washing dishes | A dishwasher on a hot cycle is fine; otherwise rinse in cooled boiled water |
| Laundry | Normal use is fine |
| Pets | Give them boiled water too |
| Filling a fish tank | Do not — and note that boiled water still contains chlorine unless treated |
When it ends
A notice is lifted once the supplier has flushed and, where needed, disinfected the affected network, and has clear microbiological results — typically two consecutive satisfactory sample rounds, which takes at least 48 hours. Suppliers notify affected properties directly when it is lifted.
After a notice is lifted, run each cold tap for a few minutes before use, and flush any appliance with a water connection — ice makers, water dispensers, filters. Replace filter cartridges that were in use during the notice.
Can I use a water filter instead of boiling?
Only if it is certified for microbiological reduction — NSF/ANSI 53 for cyst reduction, or NSF/ANSI 55 Class A for UV. Most jug filters are not, and a carbon filter can itself harbour bacterial growth. Boiling is more reliable.
Is bottled water necessary?
No, provided you can boil. Bottled water is a convenience, not a requirement.
How much water should I boil at once?
Boil what you need and store the rest covered in the fridge. Boiled water has no disinfectant residual, so it can be recontaminated — use it within 24 hours.
My water looks and tastes fine. Do I still need to boil?
Yes. Microbiological contamination is not visible, and cannot be tasted or smelled at levels that cause illness.
Sources
- World Health Organization — Guidelines for Drinking-water Quality. Public but restricted · CC BY-NC-SA 3.0 IGO
- Drinking Water Inspectorate — Drinking water quality in England and Wales. Open — attribution required · Open Government Licence v3.0
- UK Health Security Agency — Waterborne infectious disease surveillance and guidance. Open — attribution required · Open Government Licence v3.0