So-called “dry spills” are illegal because they can cause harm to the environment and can lead to a higher concentration of sewage in waterways.
Southern Water, which supplies water for much of Sussex, was one of the three companies whose data was analysed by the BBC.
The company serves millions of people with water and waste services.
Analysis by the BBC released today found that there were 63 dry spills last year.
The spills ran for a total of 792 hours.
In one case study, a dry spill found by BBC analysis was backed up by Robert Bailey from the Clean Harbours Partnership who noticed his local chalk stream, the River Lavant near Chichester, had become “discoloured for many miles and was starting to fill with a white plume”.
His concerns correlate, from March last year, correlate with two dry spills the BBC identified at the site.
John Penicud, head of wastewater at Southern Water, told The Argus: “So called ‘dry spills’ are a complex issue. Water is a powerful force of nature – and high groundwater conditions can lead to rising water finding the path of least resistance into a network of sewer pipes and manholes, and a discharge made up of groundwater is not caused by rainfall and can happen in dry weather. It is required to be reported as a ‘spill’.
“The problem is especially challenging in areas prone to flooding, as mitigation measures such as sewer relining and manhole sealing redirect flows and groundwater can then cause flooding. Private, illegal connections to the system are another potential source.
“We work with the Environment Agency and stakeholders to cut these so-called ‘dry spills’ – and all forms of water and wastewater releases.
“Our nature-based solutions are already showing promise in reducing dry spills and we are doing this at Lavant and other sites.
“We are engaging with our regulators and stakeholders to develop plans for cleaner rivers and seas, and we are funding £3 billion to improve the environment and give our customers the service they deserve. Our shareholders have injected more than £1.5 billion since 2021 to fund this work.
“At Ham Lane, a pumping station on the River Ouse flood plain south of Lewes, we will be investing £3.4 million in nature-based solutions such as sustainable drainage, tree planting and water gardens.
“Lavant is in a catchment that is particularly prone to groundwater infiltration. It is already benefiting from the creation of a wetland at the rural wastewater treatment works which greatly reduces the impact on the seasonal ‘winterbourne’ river. We plan to invest £1.6 million on relining more than 4km of sewers in the catchment but the site will still be affected by groundwater entering private sewer pipes.”