Water infrastructure failure or loss of drinking water

Impact 5
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upper likelihood error bar risk indicator
lower likelihood error bar
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Impact & Likelihood
Impact key
5 Catastrophic
4 Significant
3 Moderate
2 Limited
1 Minor
Likelihood key
5 >25%
4 5-25%
3 1-5%
2 0.2-1%
1 <0.2%


The failure of one or more water treatment works in one region would result in the loss of key public water supply and wastewater services. The water sector has established contingency plans to mitigate a range of water supply incidents. This includes mutual aid capability across the water companies and the provision of alternative water supply, which would prioritise the most vulnerable communities.


The reasonable worst-case scenario would involve the sudden loss of piped water supply, or the degradation of the piped supply such that it was unfit for human consumption even after boiling. The loss of water would have knock-on consequences to the functioning of essential services such as schools, hospitals and prisons until alternative water supplies are provided or supply is restored.

Key assumptions

It is assumed this would be a regional event with loss of drinking water output from one or more water treatment works and there would be limited capability in the water network to reroute supplies from other treatment works.


There are different scenarios that could result in the loss of water supply, including burst water pipes or extreme weather incidents, however the capabilities required to minimise the impacts would remain broadly the same.

Response capability requirements

Water companies in England are required to plan for disruptive scenarios and would seek to use a number of mitigations including rezoning of their network, tankering water from alternative treatment sites, the use of mutual aid from other water companies and the provision of an alternative water supply to affected consumers as soon as possible, but within 24 hours. Alternative water would be prioritised to vulnerable consumers and sites with larger numbers of vulnerable individuals (such as prisons and care homes). Water is a devolved matter and Wales, Northern Ireland and Scotland have equivalent requirements in place.

Water companies would support the local response, which would be coordinated by the local resilience forum and the Department for Environment, Food and Rural Affairs should a national response be required.


Piped supply would be restored as soon as possible but would be dependent on the extent of the infrastructure damage. Consumers are likely to be gradually brought back on to supply in stages as their area is reconnected. Throughout this time, alternative supplies via bowsers and bottled water stations would be maintained.