Southern Water made the shocking discovery at Premium House in The Esplanade, Worthing – which is only 100 metres from the water.
Eight of the flats were incorrectly plumbed into surface water drains rather than the sewer, meaning all household wastewater, including sewage, was being discharged onto the beach.
The owner of the block rectified the misconnections within hours of the problem being found.
Nearby bathing site Worthing Beach House has been rated poor, the worst rating for water quality, since it was first designated in 2024.
The Environment Agency believes contamination of surface water drains is a cause of pollution there.
This contamination can be caused by misconnections, as well as pollutants being poured directly down drains by businesses and members of the public.
A misconnected toilet can pour 20,000 litres of sewage a year into the nearest water course, or even straight onto the beach, a spokesman for Southern Water said.
The water company investigates these misconnections, also known as illegal connections.
Sussex’s Southern Water investigators Will Curtis and Pete Booth, who The Argus met last year, were the ones to track down the misconnection at Premium House.
Will Curtis, left, and Pete Booth, right (Image: The Argus)
When misconnections are found, property owners are asked to make the simple fix to attach pipes to the sewer so water from dish or clothes washers, showers or toilets goes to the sewer for treatment.
Phil Cresswell-Nash, bathing water partnership manager at Southern Water, said: “Everyone involved is working very hard to find and resolve issues at the newly designated bathing water at Worthing Beach House – council teams, the Environment Agency and local groups.
“But no one has been working harder than our own sewer Sherlocks – the misconnections team.
“Pete Booth and Will Curtis have made an amazing find here with eight flats mistakenly connected to a surface water drain instead of our sewer.
“The owner responded incredibly rapidly and put things right and this will make a real difference to water quality at Worthing Beach House.
“Lots of things can contribute to bathing water quality – our assets and storm water releases can have an impact. But misconnections and run off from roads are also very important.
“In addition to the painstaking detective work by the misconnections team, Southern Water has been examining its own sewers for damage using CCTV and have fixed a number of leaks that could have led to wastewater leaching into drains.”
Tom Rutland, MP for East Worthing and Shoreham, said: “Last year, I was pleased to see that Shoreham and Southwick’s beaches were rated as excellent, and Lancing Beach Green was rated as good – but it was extremely disappointing that Worthing Beach House was still classified as poor.
“It is important to also recognise when progress is made.
“I welcome the news that the Environment Agency and Southern Water have worked collaboratively to successfully identify and quickly fix this significant illegal connection to prevent further sewage discharges into the sea at Worthing.
“Cleaning up our rivers and seas is an absolute priority for me, and since being elected, I have met with Southern Water executives on multiple occasions to hold them to account, and raised issues around sewage discharges in the House of Commons and directly with ministers.
“Our Water (Special Measures) Act has banned unfair bonuses for water bosses, introduced new fines for polluting water companies, and ringfenced bill increases for investment in our water infrastructure.
“After years of underinvestment, it will take time to clean up our rivers and seas, but the government has taken more action than any before it to ensure that we do.”