Southern Water

As a swimmer, I hate the idea of polluted rivers, beaches and seas. We know that water firms need to undergo a sea change in behaviour. This Government is mandating that they do so. In the next two decades, the water utility firms will be investing £56 billion to dramatically improve the cleanliness of our rivers, beaches and seas. Specifically, they are being told to deal with the issue of storm overflows.

What’s the problem and what are storm overflows?

Pollution into UK rivers and beaches damages wildlife and is unpleasant and sometimes unsafe for humans. It comes in different guises. Much pollution is caused by agricultural run-off. Another form of pollution is caused by storm overflows. This is when stormwater overwhelms the drainage system and on occasion takes raw human sewage with it into rivers and seas.

Under previous governments the problem wasn’t properly monitored, so we didn’t know how bad it was, although we knew it was bad. So bad indeed that the last Labour Government was taken to court by the European Union.

According to the Environment Agency, storm overflows are:

“a result of Victorian sewer infrastructure, operating as safety valves built into the combined sewer system. They discharge excess sewage and rainwater to rivers, lakes, or the sea when the sewer system is under strain. This protects properties from flooding and prevents sewage backing up into streets and homes during heavy storm events. A growing population, an increase in impermeable surfaces and more frequent and heavier storms because of climate change have increased pressure on the system.

There are around 15,000 storm overflows in England. They discharge at different rates depending on local conditions including climate, rainfall and the type of sewerage system. In 2021, 90% of storm overflows discharged at least once, with 5% discharging more than 100 times, including in high priority nature sites such as Sites of Special Scientific Interest. Bathers and other water users are impacted by the 8% of storm overflows that discharge near a designated bathing water.

High levels of sewage discharges present two main types of harm:

Harm to public health

Discharges from storm overflows contain raw sewage, which can contain high levels of harmful pathogens, such as viruses and bacteria. This can pose health risks to people who use our water bodies for recreation.

Harm to the environment

Storm overflows can also lead to ecological harm due to their impact on water chemistry. Discharges of raw sewage can contain organic pollutants, microplastics, pharmaceuticals, nutrients, and heavy metals, as well as visible litter that is flushed down toilets. The impact of sewage discharges on ecology varies depending on the pollutants it carries, their concentration, and the nature of the receiving water body. The smaller and more dilute the sewage discharge, and the larger and faster flowing the receiving river, the lower the ecological impact.”

Why is this investment happening now?

In 2021, the Government brought in the Environment Act, enforcing much higher standards for environmental protection and higher standards for water firms. Specifically, there is also now a national plan for storm overflows into rivers, beaches and seas, and a national Integrated Plan for Water, announced April 2023, to clean up water supply for future generations.

Details of all three are here:

There have been significant improvements in water quality in the past ten years. Despite storm discharges, UK bathing waters continue to improve. Last year, 93 percent were classified as ‘good’ or ‘excellent’, up from 76 percent in 2010. Supply interruptions to customers have decreased five-fold and leakage has been cut by a third since privatisation. Pollution in our rivers has significantly reduced. There is now 80 percent less phosphorus and 85 percent less ammonia compared to 1990, when water companies were privatised. Cadmium and mercury in the water environment have also reduced.

The Government’s plans will now make further progress.

Why have these changes not happened already?

In the past decade, water firms have been instructed to meet two key objectives: reducing leaks and ensuring the standard of drinking water. As to the first, water leakage had been an ongoing scandal due to the age of water infrastructure and a lack of investment when the water firms were publicly owned. Since then, some 40 percent of pipes in the UK have been replaced and UK tap water is among the cleanest in the world.

Under public ownership, the water firms invested about £500 million a year. Under private ownership that rate of investment doubled to £1 billion a year, and now, under the new Conservative plans, the rate of investment will double again.

Over the past few years, it became clear that the new focus for the next decade should be on significantly reducing the damage being done to our rivers, beaches and seas by storm overflows and other forms of pollution. This was led in Parliament by the Conservative Philip Dunne, MP for Ludlow, whose painstaking work on the Environmental Audit Committee showed the scale of the problem.

The Government have since brought in the ground-breaking Environment Act, accompanied by a plan for water and a plan for storm discharges.

How did water firms perform under the previous Labour Government?

Disgracefully, water firms under the previous Labour Government were given permission by Labour to self-monitor. This represented a clear conflict of interest between the Labour Government and privatised utility firms that Labour MPs professed to dislike.

As my MP, what have you done about it?

As your Member of Parliament, I persuaded Southern Water to make the Isle of Wight an example of best practice nationally. This means prioritising the Island both for funding and for projects to significantly reduce the amount of water entering the sewers during storms. 

Millions of pounds - with millions more in the pipeline - have been committed to schemes big and small, including £13.5 million for Sandown Water Works, £2.5 million for work at Knighton, £5 million for Carisbrooke and over £7 million for works in Cowes, Newport and Brading. The full list is below.

In total, Southern Water will, on current figures, invest over £60 million in a series of projects across the Island, with more money expected to be pledged in the coming months and years.

What is Southern Water’s pathfinder project?

The Isle of Wight is now one of a small number of Southern Water ‘pathfinder’ projects for reducing sewage discharges. The project involves an investment programme designed to significantly reduce sewage and storm overflows into rivers, beaches and seas around the Island.

The first trial of the pathfinder project, a project in Havenstreet, is now complete. Approximately two thirds of Southern Water customers in Havenstreet took part in the scheme. Before the trial, Havenstreet pumping station spilled 20-30 times per year. Southern Water has increased the pumping rate of Havenstreet pumping station; installed 147 slow-release water butts; and diverted the roof drainage of 5 large roofs into planters. The scheme has resulted in a 70 percent reduction in local storm overflow activity.

Southern Water is now working on similar improvement works in Gurnard and Cowes. This includes plans for the installation of 2,245 slow-release water butts. Further work will follow in Fishbourne, Wootton, Yarmouth, Freshwater, and East Cowes.

Proposals published by Ofwat in April 2023 would allow Southern Water to invest even more in the Island as part of a region-wide £50 million investment programme to reduce the use of storm overflows between 2023 and 2025. The plans would see Southern Water continue its trial of raingarden planters, swales and tree pits, and construction of wetland areas.

In total, between 2020 and 2025, Southern Water will invest £31.4 million in maintaining its water supply assets on the Island, and over £30.5 million in maintaining and improving wastewater treatment assets on the Island.

The investment in water supply assets includes pump, tank and treatment improvements at Sandown Water Supply Works and a major programme of other water supply refurbishments. The wastewater treatment programme will see improvements to numerous wastewater treatment works to increase treatment capacity and prevent sewage discharges; increases in stormwater capacity at key treatment works; and other upgrades to reduce phosphorus discharges. A full list of projects is included below.

Furthermore, between 2025 and 2030, Southern Water has set out plans for a major water recycling project on the Island. This will allow the Island to recycle more of its own water supply and gain greater independence from the mainland UK. Planning submissions are set to be completed in January 2024. The treatment plant is forecasted to be operational by the end of 2026.

I will continue to work with community groups, councillors and Southern Water to make sure we maintain and improve our Island’s environment – this is all part of getting a better deal for the Island.


Southern Water pathfinder project – planned improvements


Optimisation of sites

October 2022 – January 2023

Removing 3 misconnections

March 2023 – August 2023

Diverting the drainage of 31 large roofs

January 2023 – March 2023

12 highway schemes to install highway sustainable drainage

September 2023

Installing 2245 slow drain water butts

January 2023 – March 2023


Fishbourne and Wootton

Optimisation of sites

February 2023

Removing misconnections


Diverting the drainage of 12 large roofs

January 2023 – March 2023

1 highway scheme to install highway sustainable drainage

September 2023

Installing 630 slow drain water butts

January 2023 – March 2023


Yarmouth and Freshwater

Optimisation of sites

March 2023 – June 2023

Removing 2 misconnections

August 2023 – December 2023

Diverting the drainage of 24 large roofs

May 2023 – July 2023

7 highway schemes to install highway sustainable drainage

September 2023

Installing 1700 slow drain water butts

May 2023 – July 2023


East Cowes

Optimisation of sites

January 2023

Removing 2 misconnections

August 2023

Diverting the drainage of 31 large roofs

January 2023 – March 2023

6 highway schemes to install highway sustainable drainage

September 2023

Installing 3245 slow drain water butts

January 2023 – March 2023



12 schools on Isle of Wight will receive SuDs (Sustainable Drainage System) for schools support during 2022/23:

  • Soakaways and planters that harness the run-off from roofs to prevent flooding.

  • Learning opportunities about the flow of water into the ground alongside in class learning about the importance of nature-based solutions to manage flooding and run off.



Southern Water asset management investment, 2020-2025

Water supply investment





Sandown Water Supply Works

Pump, tank and treatment improvements. Report confirming commissioning of Clear Water Tank and High Lift Pumps.

£11 m

Nov 2025

Installing eel screens to prevent eel trapping.



Carisbrooke Water Supply Works

Installation of a fish pass to aid fish migration.



Pumping, dosing and storage refurbishment.


Totland Water Booster Station

Pump, dosing and control refurbishment.



Knighton Water Supply Works

pH correction.



Cowes, Newport and Brading water supply zones

Pipe relays, flushing and monitoring: First Phase of flushing complete; Second Phase to be complete by year end 2025.


End 2025

Ventnor Water Supply Works

UV dosing and refurbishment. UV complete, ongoing improvement program by year end 2025.


End 2025

Cooks Castle reservoir

Full structural refurbishment. Cleaned & inspected, refurbished and repaired – complete. Awaiting reintroduction replacement asset.


Mostly complete

Greatwoods reservoir

Full structural refurbishment.


Inspection and assessment in progress; rezoning and enabling being undertaken


Waste water investment

Site Unit Title




Brighstone WTW

Increase flow to full treatment to prevent spills to storm during dry weather.



Calbourne WTW

Increase flow to full treatment to prevent spills to storm during dry weather.



Upgrades to WTW to achieve lower Phosphorus discharge limit of 0.5mg/l Annual Average.

Godshill WTW

Transfer all flows to Sandown WTW.



Roud WTW

Increase flow to full treatment to prevent spills to storm during dry weather.



Upgrades to WTW to achieve lower Phosphorus discharge limit of 0.3mg/l Annual Average.

Divert storm relief sewer to WTW inlet works.

Sandown New WTW

Increase flow to full treatment to prevent spills to storm during dry weather.



Increase permitted Dry Weather Flow limit to accommodate population growth.

Increase storm storage tank capacity.

Shorwell WTW

Increase storm storage tank capacity.



St Helens WTW

Increase flow to full treatment to prevent spills to storm during dry weather.



Wroxall WTW

Upgrades to WTW to achieve lower Phosphorus discharge limit of 0.25mg/l Annual Average.



Appley Park

Sewer repair.




Replacement of the CHP engine at Sandown to maximise energy generation and comply with new environmental legislation.