Water regulator, Ofwat, said more than 200,000 customers did not have water supply for more than four hours and tens of thousands were left without supply for days during the period of cold weather in late February and early March.

In its review into how water companies responded to the cold snap, Ofwat identified failings such as poor preparation and planning, limited or inaccurate data, and poor communication with customers.

Ofwat has asked four water companies – Thames Water, Severn Trent, Southern Water and South East Water – to submit a detailed, externally audited, action plan setting out how they are addressing the issues identified.

Ofwat chief executive, Rachel Fletcher, said: “The freeze and rapid thaw earlier this year was forecast and was not unprecedented. A number of water companies showed what can be done to serve customers in the face of bad weather. But too many companies were caught off guard and let people down, causing real hardship as a result. Our report shows there is no excuse for this level of failure.

“Four companies have three months to satisfy us that they will be ready to perform at the level customers deserve the next time there is bad weather. We will take action if they don’t rise to this challenge. We expect every water company to take action on the back of this review and the industry as a whole to transform how it works together in situations like these.

“Water is an essential service. Water companies must be prepared for whatever the weather brings.”