A Guardian investigation with Watershed Investigations and River Action found that UK water companies reported at least £1.4 billion in revenue from accepting industrial wastewater over six years. The reported total includes £336 million in 2025–26; the actual figure may be higher because South West Water did not disclose its trade-effluent revenues.

The investigation compiled 26,131 industrial wastewater consents. Together, they could allow up to 607.6 billion liters of trade effluent to enter sewage-treatment works in a year. Thames Water had the largest identified permitted volume, at about 113 billion liters annually, followed by United Utilities at 104.6 billion liters.

The report raises concern that many sewage works rely on biological treatment designed mainly for domestic sewage, which may not remove certain industrial chemicals. The investigation said wastewater accepted by treatment works may contain substances including PFAS, solvents, pharmaceuticals and heavy metals. Contaminants that remain after treatment can reach waterways in effluent or be carried in sewage sludge.

The system also has an oversight gap, the investigation said: water companies set and enforce individual trade-effluent consents, with no independent regulator overseeing those consents and no central national register. The Environment Agency said the framework dates back more than 30 years, before many current concerns about contaminants such as PFAS were fully understood.

The findings have renewed calls for stronger monitoring, transparency and accountability. The UK government said water companies should not profit from pollution and that it intends to reform wastewater regulation. Water companies maintain that trade effluent is accepted under regulatory requirements and that charges contribute to treatment costs.