Water firms “passed” thousands of pollution tests under a self-monitoring regime … yet the tests were never even conducted, the Observer can reveal. The water firms’ own operational data for sewage plants across the country reveals how outflows of effluent had stopped – in some cases for just a few hours – on days that samples were supposed to be taken. Despite testers being unable to check whether firms were allowing too much pollution to flow into rivers, the Environment Agency rules allowed these “no-flows” to be recorded as compliant with the environmental conditions of their operating permits. Southern Water has already previously been found to have “deliberately manipulated” the effluent flow to avoid pollution detection. The number of no-flows it reported plummeted after its practices were investigated. Peter Hammond, from the campaign group Windrush Against Sewage Pollution (Wasp), has conducted an analysis of no-flow events from 2021 to 2023 where the sewage plants were deemed to be compliant with their permits. He says such incidents should be properly investigated by the regulator and the regime should be overhauled. “Water companies cannot be allowed to mark their own homework,” he said. “Monthly manual testing of treated sewage must be replaced by continuous automated sampling. Default assumption of permit compliance in the face of failed sampling is totally unacceptable.” After being contacted by the Observer, the Environment Agency said it was changing its rules. The new changes to shut down the loophole will be made in early 2025. Ministers last week announced an independent commission into the water sector and regulation, in what is expected to be the largest review of the industry since privatisation. The water regulator, Ofwat, could be overhauled or even abolished. Water firms are allowed to “self-monitor” for pollution incidents under a controversial scheme introduced in 2009. The samples for lab testing are typically taken by water firm employees and are in addition to audits conducted by the Environment Agency. The environmental performance of firms is linked to bosses’ remuneration and the cost of bills. Under the “operator self-monitoring system”, between 12 and 24 samples are taken from the outflows of sewage works each year to check if the treated effluent complies with the conditions of their environmental permit. In the event that no effluent is flowing, the plant is reported as compliant with its permit, providing the employee taking the sample is satisfied with the evidence of no flow. In October 2019, Ofwat announced that Southern Water would pay £126m in penalties and rebates for breaches of licence conditions, including what it described as “artificial no-flows” at sewage plants on some sampling days. It said information on the dates of sampling by employees was supposed to be confidential, but the dates were easily predicted. It said in its deliberation: “As a result of this manipulation, a false picture of Southern Water’s [wastewater] performance was provided internally within the company, to the Environment Agency and to Ofwat.” Ofwat calculated that Southern Water avoided price review penalties of £75m because of the manipulation. Once Southern was under investigation, the number of no-flows it reported fell from 124 in 2017 to 12 in 2018. From 2021 to 2023, there were about 120,000 samples taken at sewage plants in England, with about 5,000 recorded as no-flows. Wasp has compiled 18 examples at 14 plants involving seven water firms from 2021 to 2023 where no-flows were reported on the day that a sampler arrived. In some cases, previous tests had already shown the plants were at risk of breaching or had breached the environmental conditions of their permits. Wasp says the agency should properly investigate the reasons in each case and it is unacceptable that the plant was deemed to be compliant when no samples were taken. The water firms claim there were various legitimate reasons for the no-flows, which they have investigated. These include a blockage, a power cut, planned maintenance, tankering of sewage to other plants and intermittent flow. They say there are strict safeguards to prevent manipulation of operator self-monitoring or abuse of the system. A Water UK spokesperson said: “It is up to the regulator to set the rules on testing, and for companies to follow whichever regime they impose. The current approach has tightly-controlled requirements that include detailed obligations about the timing and frequency of samples, and how they should be taken.” The Environment Agency said the rules were being updated from 1 January, which would require water firms to reschedule a sample in the event of no flow of effluent from the plant. Water firms will be required to document when and why no-flows have occurred and make this available for subsequent audit by the agency. The agency said that. on average, about 5% of samples a year are no-flows and this compares with no-flow rates when the agency took the samples. Officials say a water company may legitimately choose to tanker flows away from a plant rather than allow poor quality effluent to be discharged. An Environment Agency spokesperson said: “We investigates no-flow samples where there is a risk to the environment or if we suspect that an offence has occurred.” It is already carrying out its largest ever criminal investigation into potential widespread non-compliance by water companies. It is also recruiting up to 500 additional staff and increasing compliance checks. Ofwat said it would review Hammond’s report. A spokesperson said: “We have ongoing enforcement activity against all 11 water and wastewater companies. As part of this investigation, we will consider whether they are fulfilling their obligations to protect the environment and minimise pollution. All relevant evidence will be taken into account.” Southern Water said it instituted a “root-and-branch” review after the failings identified in the Ofwat report in 2019. “Processes and systems were radically changed to ensure that all no-flow events were genuine,” a spokesperson said. “We remain committed to transparently providing the best possible data and disclosure.”