Water companies often release illegal levels of a toxic pollutant into rivers in breaches that go undetected because of a flawed “self-monitoring” system, analysis for The Times suggests.

Rhys Blakely www.thetimes.co.uk 

The research indicates that the Environment Agency (EA) has told the companies to test the treated sewage they release into watercourses during the hours of the day when they are most likely to comply with their permits.

Outside the hours when testing happens, levels of ammonia in the treated sewage, which can wreck river ecosystems, often appear to exceed legal limits.

The findings raise serious doubts over how the EA has directed water companies to monitor their own performance. They also raise the possibility that households are being overcharged because Ofwat, the water regulator, is using flawed pollution data provided by the companies when it carries out price reviews that control consumer bills.

The Times has launched the Clean It Up campaign to press for more action on cleaner rivers, lakes and beaches. It calls for water companies to be stripped of self-monitoring powers and the job handed to a beefed-up EA.

Under what is known as operator self monitoring (OSM), companies are asked to test their own treated sewage. They typically take samples from treatment works either 12 or 24 times a year. They test for a variety of pollutants and report the results to the EA, which passes the information to Ofwat.

The analysis focuses on ammonia, which can fuel algal blooms that choke river wildlife. Official guidance from the EA says that most OSM samples should be taken between 9am and 3pm, Monday to Friday, with one in every 12 samples taken outside of these “office hours”. The readings generated by the OSM scheme suggest that more than 97 per cent of treatment works comply with their permits.

However, another set of testing data generated for internal company use — not reported to the EA and not usually made public — gives a much more detailed picture of how the plants are performing, by collecting information on ammonia levels in treated sewage every 15 minutes around the clock.

These “continuous’ readings were obtained for more than 500 treatment works, operated by six companies, by the campaign group Windrush Against Sewage Pollution (Wasp) using freedom of information laws.

The more detailed data shows that ammonia levels often dip to their lowest concentrations between about 8am and 2pm — which coincides with when the vast majority of OSM samples are taken. Outside of this testing window, ammonia concentrations are often far higher.

The OSM data suggests that less than 3 per cent of treatment works break their permits for ammonia. By contrast, the continuous data suggests that 105 out of the 531 sewage works included in the analysis — about 20 per cent of them — are in breach.

For example, in 2020 OSM samples were taken from the Chelmsford sewage works, which is run by Anglian Water, only between about 10am and 2pm. The more detailed continuous monitoring data suggests that ammonia levels often breached the permitted levels outside of this window.

The analysis is the latest to be produced by Professor Peter Hammond, of Wasp. He has previously used water company data to detect thousands of spills of untreated sewage, including many that were illegal and not picked up by the EA.

Hammond said: “If rivers are to return to at least good chemical status and customers are to pay fair charges, then Defra must stop operator self-monitoring in the water industry and replace it with well-funded, technically savvy and independent regulation.”

Penny Gane, the head of practice at Fish Legal, an advocacy group, said: “The reality is that a water company employee taking a final effluent sample once a month during a small window does not give a full picture of what’s going on at a treatment works.

“While the water companies may technically be compliant with OSM conditions in their permits, they miss peak usage times in the morning and evening when everyone is flushing their toilets, washing their clothes and showering. Breaches can go undetected by the regulator with the current approach.”

Data was supplied by Wessex Water, Thames Water, Southern Water, Yorkshire Water, Anglian Water and Welsh Water. The companies stressed that they carry out their OSM testing in line with government instructions. They strongly denied deliberately timing samples to meet their permits.

A spokesman for Water UK, which represents water companies, said: “Testing regimes are approved by the Environment Agency. Crucially, this includes the timing and frequency of samples and the rules about how they should be taken.

“In addition, water company sampling teams do not have access to the sampling programmes so they physically cannot advise operational teams of when samples are going to be taken.”

An Environment Agency spokesman said: “The Operator Self-Monitoring approach is independently accredited by the United Kingdom Accreditation Service – and practically it is only water companies that can do this level of monitoring. Under the ‘polluter pays’ principle they should also be the ones paying for it. Many other industries use similar self-monitoring, including oil and gas and the chemicals industry.

“This is not the only way we check that water companies are complying with their permits — we also do our own monitoring and on-site inspections, both announced and unannounced.”

Wessex Water took issue with Hammond’s analysis, saying that it was not possible to make “a meaningful comparison” between the data from continuous monitoring and the OSM data. In response, Hammond pointed out that OSM readings for ammonia levels at Wessex treatment plants looked at in his analysis closely match those from continuous monitoring.

Sir Dieter Helm, professor of economic policy at the University of Oxford, said: “Peter Hammond’s work is excellent. The fact that it takes a retired mathematics academic to reveal what’s going on is itself a damning indictment of what the EA and the water companies have been up to. Worse still is the fact that companies like Severn Trent refused to release the data to Peter that others at least provided. No one seems to want to take responsibility. No heads have rolled.

“Public trust is now so low that only a transparent publicly available data monitoring system will do. Defra and the EA and the water companies should finally make the shift from the analogue self-reporting farce to a 21st-century digital real-time monitoring of the sad state of our rivers.”

Severn Trent Water, South West Water and United Utilities declined the freedom of information request and withheld data.

The Times is demanding faster action to improve the country’s waterways. Find out more about the Clean It Up campaign.

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