Wild swimming what you need to know

Wild swimming – what you need to know 

Wild swimming is an activity that takes place in some natural waters, such as rivers and lakes.

It’s important for wild swimming enthusiasts to know that there are a number of factors that affect river water quality.  Water companies can have an influence, along with other activities such as agricultural practices, septic tanks and road drainage, too.

Treating your waste water

Every day we treat sewage and waste water at our water recycling centres.

Most sewage is organic which is why we use natural, organic processes to treat it, which involves bacteria breaking down waste. This treated waste water is then released back into the sea and streams, which will include bacteria. Our diagram below explains the process.

Our water recycling centres are almost 100% compliant with environmental standards, which means there is no adverse effect on wildlife.

The purpose of treatment processes is to achieve standards that protect the environment rather than public health.

Water recycling process

  1. removal of debris, rags and large objects using screens
  2. separation of solids in settlement tanks. Solids sink to the bottom and are removed as sludge. At many sites we also use chemicals to help enhance the removal of unwanted nutrients, such as phosphorus
  3. biological treatment of sewage – the liquid passes through media on which bacteria grow, such as filters of stone or plastic. The bacteria feed off the waste, helping to clean the water
  4. we also use an alternative form of biological treatment – the activated sludge process – where bacteria are mixed with the waste in large tanks using equipment which either blows or beats air into the mixture
  5. final settlement process – treated effluent enters tanks 5 where any remaining solids settle, leaving behind water which is ready to be returned to the environment
  6. at many of our sites by the sea we also have a final disinfection stage to remove bacteria which could potentially be harmful to bathers
  7. we treat this in anaerobic digesters
  8. to produce agricultural fertiliser and renewable energy.

Could things be done differently?

At some popular coastal sites, additional disinfection treatment (using ultraviolet light) has been installed at  our water recycling centres to meet  increased public health standards required. This comes at significant cost to the environment in terms of tonnes of CO2 emitted from the increased energy use of this disinfection process. We currently use as estimated 3,843,000 kWh to power this UV equipment. Most of the sites are required to dose 24/7 throughout the year even when no-one is benefitting from it.

Taking a similar approach at inland treatment sites – to kill bacteria to meet bathing water standards – would cost many hundreds of millions of pounds to build suitable treatment processes and millions of pounds to operate each year. 

In addition, the environmental impact would be thousands of tonnes of additional CO2e (carbon dioxide equivalent) emitted each year. This is diametrically opposite to the direction of travel that we as a business and as a country are trying to achieve to combat our climate crisis. As a business we have committed to achieve a net-zero carbon footprint by 2030 – some 20 years ahead of the whole country.

Disinfecting at these sites to reduce the public health risk for swimmers would need support from customers, the Environment Agency and Ofwat. It is not just a water company decision, but we’re happy to engage with those who are thinking about bathing water designation for inland rivers.  

Protecting homes from flooding

Our combined sewer overflows (CSOs) play an important and essential role in our sewerage system, as our combined sewers transport sewage from homes and industry as well as carrying surface water run-off from gutters, drains and some highways.

Heavy or prolonged rainfall can rapidly increase the flow in a combined sewer until the amount of water exceeds sewer capacity. CSOs act as relief valves, allowing excess stormwater to be released to rivers or the sea. This protects properties from flooding and prevents sewage backing up into streets and homes during heavy storm events.  

As CSOs should only operate during periods of intense rainfall, any foul water released from them will be very dilute because of the large volumes of rainwater within the system. Rarely is a pollution incident attributed to a CSO operating correctly as there is no significant environmental impact in terms of ammonia, suspended solids and biochemical oxygen demand. 

Flows are further diluted by the receiving watercourses that will also be swollen by the same heavy rain. Many CSOs are fitted with screens or scumboards that prevent debris entering the watercourse or have attenuation tanks which also improve water quality. 

We currently monitor around 75% of CSOs and have a programme in place to install monitoring equipment on all CSOs by 2023.

Through our Coastwatch service we publish information on our website and provide this information to organisations, including Surfers Against Sewage and local authorities, when CSOs have been in use. This data feeds into the Surfers Against Sewage ‘Safer Seas’ app and is available from our website outside the bathing season.

Our online mapping system shows the location and historical frequency of operation of CSOs.   

Could things be done differently?

In an ideal world we wouldn’t have a combined sewerage system, but many sewers were laid hundreds of years ago with areas, including town centres, built on top of the network of pipes. To upgrade the system is simply not feasible without demolishing buildings, causing serious disruption, and investing substantial sums of money.

There is risk that with a growing population and climate change affecting weather patterns, the use of CSOs could increase. That’s why we are calling on government to rule that all new developments cannot connect their surface water drainage to sewers that have sewage in them.

Other factors affecting river water quality

There has recently been a focus on the role of CSOs and their influence on local river water bathing quality. 

However, there are of course a number of sources of bacteria entering rivers from diffuse pollution sources including: 

  • agricultural and urban run-off
  • manure and slurry applications to land
  • faeces from farm animals, rodents, wildlife and pets
  • discharges from private septic tanks
  • runoff from highways and surface water drains, and misconnections (foul drainage from properties incorrectly connected into the surface water system by the homeowner).

All of these sources would need to be addressed before a river could meet a standard that’s deemed ‘safe’ for swimming.

Sewer blockages can also affect river water quality as sewage can back up in the system and run-off into watercourses. You can help reduce the likelihood of blockages by only flushing the 3Ps and following our advice.

Our catchment management work involves us working with farmers to help manage agricultural run-off to improve river water quality.  

Advice for swimmers

The Royal Life Saving Society UK provides advice on staying safe when swimming in open water.

Related information

Through the Environmental Information Regulations 2004 (EIR) we recently received an enquiry about the use of CSOs. You can read our response here.