Why are water companies dumping raw sewage in Britain’s rivers and coastal seas?

There were more than 400,000 discharges of raw sewage in 2020, together lasting more than three million hours, from water companies into rivers in England and Wales. One company, Southern Water, was recently fined a record £90 million for dumping up to 21 billion litres of untreated sewage over six years in protected seas off England’s southern coast.

To understand why this is happening, we need to understand the history of our sewer systems.

For most of human civilisation, sanitation was managed in a dry form. When people visited a latrine, their waste ended up in a drainage pit below or a cesspit nearby. Liquids were allowed to seep into the ground where nature would (hopefully) deal with any contaminants. The solids left over were often recycled directly to agriculture, providing nutrients for farmlands. This all changed, about 150 years ago, in the Victorian era.

The remains of an ancient Roman latrine, excavated in Spain.
Kristof Lauwers/Shutterstock

People migrating from the countryside to Britain’s crowded industrial cities meant more waste and longer distances to transport it to farms. International trade brought higher quality fertilisers to the UK too, destroying the market for London’s cesspool waste, as farmers preferred South American guano (bird droppings).

Then, the water closet arrived. Toilet waste no longer filled a pit that someone had to empty, it magically disappeared with the pull of a chain. London’s water use in 1850 nearly doubled in six years, as waste was carried through rudimentary sewers and open drains into the Thames. Two years later, in 1858, the effect of these raw sewage discharges was fully felt during “the Great Stink”, when the Thames was so odorous it forced Parliament to stop meeting due to the smell.

The solution came from the engineer Sir Joseph Bazalgette, who designed an integrated sewer system to carry untreated waste and rain water from across London further down the Thames where it was dumped via two outfalls. This was one of the largest engineering works of the time, with over 1,100 miles of street sewers, 82 miles of mains sewers, and four pumping stations installed.

After creating his initial design, Bazalgette doubled the diameters of the pipes, stating:

We’re only going to do this once and there’s always the unforeseen.

Direct river outfalls were later replaced by sewage treatment plants, but the sewer capacity, even after Bazalgette doubled the size of the pipes, was exceeded within his own lifetime. He may have been right, that such an enormous undertaking, at such huge public expense, could only be done once. But ever since we have been trying to patch and alter a system that continues to age and be overwhelmed.

A modern sewage treatment plant.
Sewer systems in the 21st century

After the construction of London’s sewers, local authorities began installing their own across the country. In 1945 there were over 1,400 sewerage companies throughout England and Wales. These were merged in the Water Act of 1973, simplifying the structure to just ten regional water authorities.

Investment fell from £3.5 billion in 1974 to just £1.8 billion in 1985. The sector was privatised under the Water Act of 1989, and now 32 privately owned water and sewerage companies operate in the UK today.

Privatisation has led to a balancing act, where water companies seek sufficient profit to attract investment, while also keeping water bills low enough to provide a public service. Both the bills water companies can charge their customers, and the performance measures they must meet, are agreed with government regulators. As the UK’s population grows, water usage increases, and climate change brings more rainfall in more intense bursts into sewers. This balancing act is becoming harder to maintain.

Water companies are allowed to release untreated waste water in rare circumstances when the system becomes overwhelmed, preventing damage to equipment and properties. This is often due to very heavy rainfall, blockages and unexpected equipment failures. Increasing sewage and rainwater flows mean these events are likely to become more frequent.

The amount of sewage companies are permitted to release is set by the regulators, but when companies fail to manage increased flows they may exceed the permits and be penalised with fines. If they try to hide or under-report these releases, the penalties are significantly larger. But the damage to the environment is often already done.

To reduce untreated releases and the environmental damage they cause, water companies are making efforts to address it. Thames Water recently spent £3.8 billion on a new “supersewer” for London, while not paying investors for the last three financial years. A bold move, but not one that will see future investors rush to provide capital for upgrades. Sewer systems are expensive and technically difficult to expand or change, and so it will be a slow and expensive process.

One way to ease pressure on the system – and save some of the 1.1 billion litres of water homes flush down the toilet each year – might be to resurrect elements of waste treatment from before the Victorian era.

Read more:
Eco-friendly composting toilets already bring relief to big cities – just ask London's canal boaters

Prototype flushless toilets can treat waste without water and sewer connections, by filtering waste through special membranes and sterilising it with heat. This could keep a lot of sewage out of the sewer system and prevent waste entering rivers, without needing expensive technologies. These systems can even recover energy – in the form of biogas fuel – and nutrients from waste, to provide farms with fertiliser and homes with power.

Peter Cruddas received funding from the Economic and Social Research Council (ESRC) for work on "Imagining a Sewerless Society".

Keiron Roberts has previously received research funding from Southern Water to investigate incorporating the circular economy into their wastewater practices (2016-2017). He has also received funding from EPSRC and FP7 to research biofuels from wastewater.