UK water companies collected more than £340m in revenue last year from taking industrial and commercial wastewater into sewage treatment works under trade effluent consents, according to figures compiled by Watershed Investigations with the Guardian and River Action. The three organisations built a database of 26,000 consents, giving the first ever national picture of a permitting system that has never been centrally recorded.

A permit regime policed by the companies themselves

Water companies are required by law to take industrial wastewater and to issue permits known as trade-effluent consents, although they can refuse individual applications. Once granted, those permits are issued and enforced by the water companies themselves, and environmental regulators play no direct role in the process. There is no independent regulator overseeing the trade-effluent process and no central register of the permits.

One unnamed industry expert described how little visibility outsiders have into the arrangements.

The same expert said companies have what was described as a financial incentive to accept far more toxic material than they should, and called the permit regime very old and not fit for purpose. The expert added that the Environment Agency does not know exactly how much of this waste is going into waterworks each year.

What goes in, and what comes out

An annual total of 608bn litres of industrial wastewater enters sewage works from sites including power stations, pharmaceutical plants, food factories, hospitals, abattoirs and waste facilities. Watershed has mapped every sewage treatment works and the industrial companies permitted to send waste to each one.

Most sewage works have only biological treatment facilities, which are not designed to remove industrial chemicals such as flame retardants, Pfas, solvents and pharmaceuticals. Where the pollutants end up depends on the treatment process.

• •Pollutants that survive treatment are discharged as treated effluent into rivers, lakes and seas.
• •Pollutants captured in sludge are spread on farmland as fertiliser.
• •Experts say the works are not designed to remove most chemicals, leaving pollutants to pass into rivers, seas and farmland.

The waste also adds to overloading of sewer networks that triggers raw sewage spills, which have caused outrage, protests and calls for nationalisation. Some permits in the database feature chemicals such as cyanide, chromium, cadmium and mercury.

Who earns what

United Utilities made the most revenue from industrial waste last year, at £61.6m, followed by Yorkshire Water at £48.8m. Anglian Water's revenues from receiving industrial and commercial wastewater have risen 62% in five years, and sector revenues overall are rising sharply.

Volume is a different leaderboard. Thames Water has the largest permitted industrial sewage volume, at 113bn litres, followed by United Utilities at 105bn and Severn Trent Water at 79bn litres.

The revenue figures differ in how they were drawn up. United Utilities and Yorkshire Water included revenues from tankered waste in their figures, while some other companies did not.

• •Welsh Water, Scottish Water and Wessex Water said they route commercial tankered waste through separate companies within their groups.

Tankered waste and chemical permits

Alongside piped discharges, tankers drive to sewage works carrying industrial effluents, landfill leachate and other liquid wastes. Both the Environment Agency officer and the industry expert named Davyhulme wastewater treatment works in Manchester, run by United Utilities, and Avonmouth, run by Wessex Water, as big receivers of tankered waste. The expert said carriers drive long distances to dispose of waste there.

An Environment Agency officer said landfill leachate was its greatest concern, because of the harmful chemical cocktail it can contain. Company checks on incoming loads can involve taking a sample and carrying out basic pH tests, which do not identify most contaminants. By the time something nasty is identified it has already gone through the works, the officer said, adding that ignorance is no defence.

The officer said companies should be seeking sufficient information from the producer of that waste so they can treat it properly.

In response, United Utilities said it has strict consent and control processes under regulatory requirements protecting public health and the environment, and accepts tankered waste including landfill leachate only at specifically permitted sites. Scottish Water said it assessed trade-effluent applications based on factors including sewer and treatment capacity, protection of infrastructure and staff, and environmental compliance.

NI Water said applications involving priority substances are referred to the Northern Ireland Environment Agency, and that dedicated teams sample sewer and tanker effluent to oversee compliance. An Environment Agency spokesperson said the trade-effluent framework was developed over 30 years ago, before Pfas concerns were fully understood, and that the agency is working to improve contaminant management.

A Water UK spokesperson said water companies are legally obliged to accept trade effluent and charges are set by Ofwat, and that permit conditions from the Environment Agency ignore that sewers cannot treat toxic substances like forever chemicals and mercury. Water UK said it has long called for the government to ban these toxic substances and force manufacturers to pay removal costs.

Amy Fairman, head of campaigns at River Action, said industrial pollution must not become a lucrative business for water companies, and that polluters must be made to pay. She said the public has a right to know what is being put into our sewage works and where pollutants end up, urging the government to confront the trade via the clean water bill.

The industry expert argued the UK needs a dedicated liquid-waste treatment sector rather than relying on a dilute and disperse model. A spokesperson for the Department for Environment, Food and Rural Affairs said water companies should never profit from pollution, and that the government is reforming the industry, including how wastewater is disposed of. All water companies included in this article were contacted for comment.