Media playback is unsupported on your device Media caption Ofwat's Regina Finn explains the reasons behind the rise

Average water and sewerage bills in England and Wales will rise by 5.7% from April to about £376 per household.

The average figure disguises variations between water and sewerage firms, with customers at Southern seeing an 8.2% rise and those at Dwr Cymru 3.8%.

In 2009 the industry regulator, Ofwat, announced a five-year plan of annual rises from 2010 to 2015 to help fund £22bn of investments.

Ofwat said it understood that any rises in tough times were unwelcome.

The regulator said that the average rise was made up of November's retail prices index of 5.2%, plus 0.5%.

Ofwat told the BBC that the differences in regional price hikes occurred because different companies had ongoing capital investments that needed different levels of funding, such as new large housing estates, or coastal protection, as in the case of Southern.

To cope with the cost of these projects, Ofwat has allowed some firms to increase prices by more than 5.7%.

"Inflation feeds through into water bills, and this is driving these rises," said Ms Finn in a statement on Tuesday.

"We understand that any bill rise is unwelcome, particularly in tough economic times. We will make sure customers get value for money," she said.

She said that by 2015, companies will have spent on average £935 for every property in England and Wales on services improvements, including on cleaning up rivers and beaches.

"If companies don't deliver on their investment promises, we will take action," she said.

Consumer groups have reacted with caution to the news.

"If companies benefit financially from this then they need to share that with customers and not just with shareholders," said Tony Smith, chief executive of the Consumer Council for Water.

"We'll be making sure that customers get some benefits from this and also that companies step up their help for customers with affordability problems."