The water regulator for England and Wales is to investigate why thousands of homes suffered water shortages in the wake of the recent cold weather.
Homes and businesses faced days without running water after pipes burst during a thaw which followed freezing weather conditions.
Ofwat will look at how prepared water firms were and what support they subsequently offered customers.
It said at the time that companies had "fallen well short".
Some water companies handed out bottled water as some households were without a mains supply for three days.
More than 20,000 homes were affected in London, where schools were forced to close and people were advised to take shorter showers as Thames Water repaired burst pipes.
In Wales, 3,000 properties lost supply and there were delays in distributing bottled water to certain areas.
West Midlands-based carmaker Jaguar Land Rover closed plants to preserve water for homes, hospitals and schools, while the chocolate maker Cadbury sent workers home from its Bournville plant.
Water companies are obliged by the regulator to compensate customers who have had their supply disrupted for an extended period of time.
Most companies are being more generous than the minimum compensation available under Ofwat guidelines.
- £30 for lost water supply for 12 hours or intermittent supply for 15 hours
- £25 for between 3 and 24 hours
- £50 for up to 2 days
- £100 for more than 2 days
- £30 for between 4 and 12 hours
- £50 for 12 to 24 hours
- £100 for 24 to 48 hours
- £150 for more than 2 days
Customers will not have to do anything to receive the compensation - they should receive a letter from their water companies in the coming days.
Ofwat chief executive Rachel Fletcher said the regulator expects compensation to be "fair, fast and free from hassle for customers".
Both suppliers and customers affected will contribute to the review.
"To be left without a vital public service like water - in some cases for several days - is deeply distressing, particularly for those in vulnerable circumstances, " Ms Fletcher said.
Any evidence that firms had breached their statutory obligations or licence conditions could result in regulatory action, Ofwat said.
The review is due to publish its findings by June 15.