Some of the UK's biggest water companies did not support customers properly during this winter's Beast from the East snow chaos, causing "significant hardship", Ofwat has said
The regulator said more than 200,000 customers were left without water for more than four hours and tens of thousands were cut off for days.
It accused firms of bad planning, communication and a lack of support.
Severn Trent, South East, Southern and Thames Water performed worst, it found.
The regulator also said it was concerned the £7m of compensation paid out to customers may not have been enough and that it would review existing guidelines.
Ofwat chief executive Rachel Fletcher said: "The freeze and rapid thaw earlier this year was forecast and was not unprecedented.
"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."
Speaking to BBC 5 live's Wake up to Money programme, she said: "There is a huge amount to do to learn some lessons. The industry as a whole really needs to step up to make sure the next time something like this happens, customers are much better served."
The icy spell in late February and early March led to a big increase in the number of burst water mains and in customers' own water pipes as frozen pipes thawed.
But Ofwat said that while suppliers' frontline staff worked tirelessly to fix the issues, higher up some firms lacked proper emergency response plans.
Citing survey data from the Consumer Council for Water, Ofwat identified common failings, including:
"In some cases, customers were left to fend for themselves, or depend upon the support of local bodies or volunteers," it added.
- Almost three-quarters of customers whose water supply was disrupted did not receive alternative supplies of water
- There was limited or inaccurate data on where problems were occurring and whether they had been resolved
- Only 60% of affected customers received direct communication from their supplier
- Stakeholders such as councils, schools and emergency services received "little or no" proactive communication "before, during or after the event".
Ofwat said all water companies in England and Wales needed to improve, but it has asked Severn Trent, South East, Southern and Thames Water to publish action plans by 28 September setting out how they would do better next time.
"We will take action if they don't rise to this challenge," Ofwat said of the four.
More empty promises!
