Southern Water has announced £1.5 billion investment to get to the “root cause” of sewage spills into seas and rivers.

Storm overflows, which capture rain and wastewater to stop flooding of homes and communities, will be the main focus in improvements pledged between 2025 and 2035.

The water company, which serves parts of Sussex, Kent and Hampshire and the Isle of Wight, was named as one of the four worst performing water companies by regulator Ofwat last month.

Southern Water bosses revealed its Clean Rivers and Seas plan on November 16 as they faced “tough choices” between environmental protection and minimising bills for customers.

Southern Water have overseen decades of mismanagement of our sewerage network, all the while paying the fat cats at the top huge pay and bonuses. Why should customers foot the bill?

The announcement said customers will “notice the impact reflected in their bills”.

Southern Water’s chief executive, Lawrence Gosden, said: “I’ve heard our customers’ concerns, and we take our impact on the environment seriously.

“We have a long-term strategy to 2050 that will restore and protect our regions’ rivers and coastal habitats and a large part of that will be to get to the root cause of storm overflows.

“We cannot simply switch storm overflows off. But by implementing this clean rivers and seas plan and tackling the root cause, slowing the flow of rainwater going into the combined sewer, whilst increasing capacity of our network, we can reduce their use.”

As part of Southern Water’s pledge to cut spills by 8,000 a year by 2035, the water company said phase one will invest £700 million on areas such as bathing waters and environmentally sensitive sites.

It added that by 2035, it aims for 75% of “high priority” overflows to meet Government targets and for 100% of them to meet targets by 2050.

Its Clean Rivers and Seas Task Force, made up of environmental scientists and industry experts, has also created solutions within the natural environment such as rain gardens and tree planting schemes.

Environmental charity Surfers Against Sewage said the plan was a “step in the right direction” with nature-based solutions such as wetlands being implemented.

But the marine conservation campaigners added that customers seeing this reflected in their bills was “outrageous”.

Surfers Against Sewage communications chief Josh Harris said: “Southern Water have overseen decades of mismanagement of our sewerage network, all the while paying the fat cats at the top huge pay and bonuses. Why should customers foot the bill?”

The charity added that through its water monitoring app, Safer Seas and Rivers Service, which receives sewage alerts from water companies, Southern Water has issued 14,931 alerts this year.

Mr Harris added: “They are top tier polluters and we won’t fall for their empty promises, or let them continue to profit off the destruction of our rivers and seas.”

Southern Water customers are being asked for their feedback on the plan before it is finalised with Ofwat.

Southern Water bosses also urged that “collaboration is key” for customers and local authorities to help with solutions such as sustainable drainage systems and water butts to drain rain water back into the environment.

The water firm’s shareholders have not received dividends since 2017 and its chief executive and chief financial officer both declined bonuses for the year until March 2023.