Water companies must be transparent with the public about sewage spill data, the UK’s information commissioner has warned.

John Edwards has written to the water companies calling on them to be as transparent as possible with their customers, and has asked them to disclose information related to sewage discharges every month.

Water companies have recently been uncooperative with data requests, refusing to reveal memos and data about sewage discharges.

The companies operate a monopoly, meaning customers cannot switch to another provider if they are unhappy with the service. One of the few powers the public has is to request data about sewage spills under freedom of information laws.

The true scale of sewage spills into English rivers was first revealed under data transparency laws.

In 2020, the Guardian reported that water companies discharged raw sewage into rivers on more than 200,000 occasions in 2019. The figures were obtained via environmental information requests, and traced releases of sewage from storm drains in rivers across England by all nine water companies.

Last year, there was a record amount of human waste dumped in waterways. In 2023, raw sewage was discharged for more than 3.6m hours into rivers and seas, in a 105% increase on the previous 12 months.

Edwards said: “My message to water companies is simple – put transparency first. The public has no choice but to use our water companies, therefore these companies should ensure they have every confidence in doing so. The current concerns about sewage pollution have dented this confidence, so we’re calling on these companies to be open about their activities to help rebuild this trust. It’s both their responsibility and their legal obligation.”

In May 2024, the Information Commissioner’s Office (ICO) issued six water companies – Anglian Water, Severn Trent Water, South West Water, Northumbrian Water, United Utilities and Yorkshire Water – with decision notices requiring them to disclose the start and stop time of sewage discharges.

David Black, the chief executive of the industry body Ofwat, said: “One of the prerequisites for building public trust is a culture of openness. As trust in the water sector is falling, that tells us companies have more to do. They should move to embrace open data as a matter of course, and they should be more open in sharing their plans and progress. And they should not wait to be pushed. Customers have paid companies to install monitors and collect their data. They have a right to see what it says.”

Water companies have previously refused to release information about sewage spills when there are investigations ongoing into the leaks. Recently, a tribunal case found that a legal exception, which says releasing information would prejudice an investigation, did not apply to the requested information.

Edwards said: “In the past, water companies have argued that disclosing information could prejudice ongoing investigations. It is now clear, following this tribunal ruling, that this defence should not stand in the way of transparency – just because information could be relevant to an ongoing investigation does not necessarily mean that it cannot or should not be released.”