Households in England and Wales will pay £123 more on average on their annual water bills from April, final figures show.

The rise – higher than stated last month – will see the average annual bill rise to £603, but there are significant variations between regions.

Water companies have committed extra money for investment in infrastructure, such as reservoirs, and more help for struggling customers.

However, consumer groups are warning the rise means more households will fall into debt.

Regulator Ofwat outlined forecast bill rises in December, which would cover the next five years.

But the bill rises for the year from April, announced by industry body Water UK, are higher than those announced by Ofwat as the calculations now include inflation – so account for rising prices that suppliers face.

The average bill increase equates to around £10 a month, from £40 to £50, but millions of households face even steeper rises.

Southern Water customers told they will see a 47% increase to £703 a year while Hafren Dyfrdwy and South West Water bills are rising by 32%.

Thames Water customers have been warned they will see a 31% hike and Yorkshire Water is raising bills by 29%.

Bournemouth Water customers will also see a 32% increase to their bills.

Other factors, such as whether a customer is metered and how much water they use, means the bill changes will vary considerably for customers depending on their circumstances.

Bill rises for the next five years are being front-loaded, with a big increase this April so that spending on new infrastructure, such as new reservoirs, can get going.

Water UK chief executive David Henderson said: “We understand increasing bills is never welcome and, while we urgently need investment in our water and sewage infrastructure, we know that for many this increase will be difficult.”

Water companies say they will also set aside more than £4bn to fund social tariffs – discounted bills for vulnerable people – over the next five years.

But the Consumer Council for Water (CCW), which represents billpayers, said support did not go far enough, as about 2.5 million households were already in debt to their water company.

“These rises will heap considerable pressure on millions of customers who are already having to make difficult choices,” said its chief executive Mike Keil.

“Customers want to see investment in improving services and cleaning up our rivers but that can’t come at an unbearable cost to struggling households.”

The CCW said this was the largest rise in water bills since the privatisation of the water industry 36 years ago.

David Black, chief executive of Ofwat, said: “We have pushed companies to double the amount of support over the next five-year period and strongly encourage customers who are struggling to pay their water bills to contact their water company to access this.

“While bills are rising, the £104bn investment we have approved over the next five years will accelerate the delivery of cleaner rivers and seas and help to secure long-term drinking water supplies for customers.”