Protecting homes and managing storms

In a downpour, we sometimes release storm water from our long sea outfalls - this is done to protect homes from flooding.

What are stormwater and Combined Sewer Outfalls?

In the older parts of our towns and cities built before 1960, the sewers were built with a combined function of removing both wastewater and rainwater away from houses and businesses.

In wet weather these combined sewers can become overwhelmed by rainwater. In these situations to prevent homes from flooding, to protect our pumping stations and to maintain the performance of our wastewater treatment works, it is necessary for Water Companies to release stormwater to rivers and into the sea. These releases are made through Combined Sewer Overflows (CSOs).

What is released is not "raw sewage" but wastewater (which is mainly water from washing machines, showers and dishwashers) heavily diluted by rain and run-off from roads and land.

When we release stormwater to sea it is permitted by our regulator, the Environment Agency. Southern Water is required to report to the Environment Agency about the operational performance of these overflows.

More information about how this all works can be read here

So how does this affect bathing water?

Bathing water quality can be affected for a number of reasons, especially during wet weather. Sources include run-off from roads and agricultural land, dog and bird pollution.

In recent years, we've made positive progress with bathing water quality in our region. Every bathing water in our region meets the quality standard - 55 bathing waters met Defra’s top standard 'Excellent' last year, and 23 were 'Good' while none were below acceptable.

We're also investing £31.5 million as part of our Bathing Water Enhancement Programme, further details of which can be found in the links below.

What the future holds with our CSOs

We’re making a number of improvements ourselves. In the short term, we’re investing £1.7bn over 2020-25 to improve capacity and capability of our wastewater network.

Work to improve storm overflow management includes: Event Duration Monitoring (EDM) already installed at 98% of sites with further improvements being delivered to close the coverage gap before 2023; improved flow management at wastewater treatment works where we’ve invested £13m between 2015 and 2020 to address risk to storm overflow at 29 sites and we are investing a further £13m between 2020 and 2025 at a further 36 sites to improve either instrumentation or data capture or both.

Further reading

• Recent years have seen Southern Water invest millions in its wastewater network in order to reduce its impact on bathing water quality. The company has also launched a campaign with the Environment Agency, called Beauty of the Beach, to raise awareness what affects bathing water quality and the simple steps we can all take to help protect it.

• In recent years, water quality has never been better, and of the 14 bathing water beaches on the Isle of Wight in particular 11 are excellent and the remaining three are classified as good.

• To see the latest news on our Bathing Water Enhancement Programme, visit: