Monitoring and operator self-monitoring

Commentators, journalists and water campaigners have regularly criticised something called ‘Operator Self-Monitoring’, a system that requires water companies to check and report on the quality of treated water discharged into waterbodies following the wastewater treatment process. This is sometimes characterised as ‘water companies marking their own homework’. While that phrase simplifies a tightly defined set of rules, it nevertheless captures the public’s rejection of the idea that water companies should perform this function themselves. 

What is Operator Self-Monitoring?

Operator Self-Monitoring was introduced by the Environment Agency in 2009. It requires water companies to do their own testing of ‘final treated effluent’ (the wastewater discharged into waterbodies following the sewage treatment process) that comes out of a treatment works, with the results reported to the Environment Agency. This monitoring forms one part of a system of checks run by the Environment Agency on whether pollution is under control. Specifically, Operator Self-Monitoring provides routine data on whether sewage works are complying with their environmental permits. 

The Environment Agency sets rules about how self-monitoring should be carried out. For example, samples must be taken at random intervals on different days and times of the week and sent to independent accredited laboratories. There are also controls to prevent on-site operational teams influencing the results, such as no notice of when samples will be taken. The Environment Agency then examines the results and carries out audits. The Environment Agency also conducts unannounced inspections. The number of inspections more than doubled in 2025.  

What should happen next?

Water UK has been calling for an end to Operator Self-Monitoring for several years, and this formed part of our submission to the recent Independent Water Commission. Our view is that now, more than ever, it is vital that the public can trust how water companies are regulated. Whatever the efficiencies of Operator Self-Monitoring, it is abundantly clear that the public do not have faith in it and it must be scrapped.

In response to the Independent Water Commission’s final report, last summer Defra committed to end Operator Self-Monitoring and move toward ‘Open Monitoring’. Although not fully defined, this suggests an approach that involves a much wider range of checks, sampling and data – an approach we would support.

Wider developments in monitoring

Operator Self-Monitoring deals with the continuous discharges of sewage works so is different to how ‘storm overflows’ (mixed discharges of rainwater and wastewater) are monitored. Storm overflows have digital monitors that show when they activate in real-time. Every storm overflow in England is now fitted with a monitor, providing country-wide data on when discharges are happening. One new source of data over coming years will be from the rollout of ‘continuous water quality monitors’. These will be placed upstream and downstream of points where sewage enters waterbodies, allowing the Environment Agency and public to compare in near real time the water quality before and after the point of discharge. 

These new monitors are not precise enough to check certain chemicals (such as ammonia) against the strict limits set in environmental permits. They also only cover a subset of water quality parameters. Sewage works permits cover a much wider range of pollutants. 

While continuous river water quality monitors are not a panacea, if used alongside other sources of information they should allow a better understanding of what is happening in each river. They should be further supported by citizen science, which could see members of the public more systematically trained in reliable techniques adding their own data to help inform local plans and projects, as well as emergent technology (such as AI-enabled satellite data) and more frequent and granular physical sampling of rivers by the Environment Agency. 

The data on both final treated effluent and the health of rivers should all be checked and made available quickly, reliably and transparently to the public. If Defra’s ‘Open Monitoring’ work delivers this outcome then we will have a much more comprehensive and timely understanding of the sources of harm, priorities for action and how assets are performing.