Southern Water Highlights Early Progress In Storm Overflow Reduction Plan

Southern Water has reported early progress in its £1.5 billion Clean Rivers and Seas Plan, with more than 700 storm overflow releases prevented over the past year.

The company says it will invest £341 million across Hampshire and on the Isle of Wight over the next five years, targeting almost 100 storm overflows.

More than £70 million has already been spent on a range of measures including sustainable drainage solutions, infrastructure upgrades and the use of artificial intelligence.

Work has been carried out at 95 of the most environmentally sensitive sites, with 29 projects delivered ahead of schedule.

Southern Water says the early results show progress is being made, but acknowledges that storm overflows remain a significant national issue requiring long-term investment and action.

The company is also focusing on nature-based solutions, with the majority of planned interventions designed to work with the natural environment to reduce pressure on the sewer network.

Storm overflows typically occur when rainwater and groundwater enter sewer systems, particularly during periods of heavy rainfall. In some areas, surface water from roads and roofs still flows into the same pipes as wastewater, while in others, rising groundwater can overwhelm the system.

Overflow outlets are used to prevent flooding in homes and streets, though the company accepts they are not a long-term solution.

Work Underway Across The Region

In Hampshire, a £170 million scheme in Portsmouth Harbour is now in its second year, combining sustainable drainage and efforts to divert rainwater away from sewers.

More than 200 properties in Fareham and Gosport have already had roof drainage separated from the sewer system, with further work ongoing in Emsworth.

Sewer sealing has also been carried out across the Pan Parishes near Andover to reduce groundwater entering the network.

Additional projects include tidal infiltration work in Port Solent and large-scale surface water disconnection schemes in Cosham and Drayton, areas which have historically experienced flooding.

Progress On The Isle Of Wight

On the Isle of Wight, a number of projects are already showing results.

In Cowes, pipework upgrades and smart sewer technology have prevented 57 storm overflow releases.

In Newport, previously unused storm ditches have been brought back into use to provide temporary storage during heavy rainfall.

Upgrades at Appley Pumping Station have significantly increased capacity, with storage rising from 900 cubic metres to more than 4,000, and treatment capacity more than doubling.

At the Wildheart Animal Sanctuary, a sustainable drainage “safari” system has been installed, capable of processing hundreds of thousands of litres of water each year.

Across the Island, more than 4,000 water butts, 200 rain garden planters and permeable driveways have been installed.

Work has also been carried out to prevent rainwater from 175 large roofs, including schools and businesses, entering the sewer system.

Further investigations are due to begin on the Isle of Wight from April 2026, as part of efforts to meet regulatory targets by 2035.

Proposed measures include separating surface water from sewage systems, tackling groundwater and tidal infiltration, and upgrading treatment works.

Elsewhere in the region, Southern Water says it has identified and addressed issues including a leaking sewer beneath Southsea pier and an illegal connection at a block of flats in Southampton, which had been discharging wastewater directly into a river.

Nick Mills, Director of Environment and Innovation at Southern Water, said the company is “on a really exciting journey” to improve water quality.

He added that while the challenge is complex, driven by factors such as climate change, heavier rainfall and population growth, the company is committed to working with local authorities and communities to deliver cleaner rivers and seas.

An interactive map outlining current and future projects is available as part of Southern Water’s Clean Rivers and Seas Plan.