Emergency water: what to do when supply fails
Boil water notices, contamination incidents and post-disaster supply. What works, what does not, and what makes things worse.
Boil water notices
A boil water notice is issued when there is a risk of microbiological contamination — typically after a loss of pressure, a burst main, flooding of a source, or a detection at a treatment works.
Bringing water to a rolling boil is sufficient. The pasteurisation temperatures that kill waterborne pathogens are all well below boiling point, so once water has reached a rolling boil it is safe; there is no need to boil for a set number of minutes at sea level. Boiling for longer does no harm and no additional good.
| Use | Guidance |
|---|---|
| Drinking | Boil first, or use bottled water |
| Preparing food and drinks | Boil first |
| Brushing teeth | Boil first |
| Making baby formula | Boil first; this matters most for infants |
| Washing hands | Tap water with soap is generally fine unless told otherwise |
| Bathing and showering | Generally fine for adults; avoid swallowing. Take care with young children |
| Washing dishes | Dishwasher on a hot cycle is fine; otherwise rinse in boiled water |
| Pets | Give them boiled water too |
If you have no supply at all
- Use stored water firstWater stored in clean sealed containers is the safest option and requires no treatment.
- Identify the least contaminated source availableRainwater collected in a clean container, then flowing water, then still water. Avoid anything near sewage, industry, agriculture or flooding.
- Remove particlesLet it settle, then pour off the clear water, or filter through cloth. This is essential before any disinfection — disinfectants cannot penetrate particles.
- DisinfectBoiling is the most reliable and needs no equipment beyond heat. Chemical tablets, unscented household bleach at the dose on the label, or a filter with an absolute pore size of one micrometre or less are alternatives.Chlorine-based disinfection does not work against Cryptosporidium. Boiling and adequate filtration do.
- Store safelyClean, covered containers. Use within 24 hours where possible, since disinfected water without a residual can be recolonised.
Storing water at home
- Around three litres per person per day covers drinking and basic food preparation; more is needed for washing
- Three days is a common planning minimum; a week is better where supply is less reliable
- Use food-grade containers, filled with tap water, sealed, and kept cool and out of sunlight
- Rotate every six months. Mains tap water is not designed for long storage and its chlorine residual dissipates
- Do not reuse containers that held milk or fruit juice — residues support bacterial growth
After a flood
Assume flood water contains sewage. If your property has been flooded and you are on a private supply, do not use it until it has been tested and disinfected. On a mains supply, follow your supplier’s advice — a boil water notice may be issued if pressure was lost. Clean and disinfect any surfaces and containers that flood water touched.
Sources
- World Health Organization — Guidelines for Drinking-water Quality. Public but restricted · CC BY-NC-SA 3.0 IGO
- UK Health Security Agency — Waterborne infectious disease surveillance and guidance. Open — attribution required · Open Government Licence v3.0
- Drinking Water Inspectorate — Drinking water quality in England and Wales. Open — attribution required · Open Government Licence v3.0