Southern Water cut leakage sharply during 2025/26, but still lost almost 90 million litres of treated water every day — enough over the year to fill Bewl Water reservoir and carry on leaking. Behind that eye-watering total sit 12 serious pollution incidents, wastewater permit compliance of just 54.2%, financial controls Deloitte wouldn’t rely upon, a headline loss £15.7 million below the audited figure and a turnaround kept afloat by higher bills, £900 million from shareholders and almost £2 billion of new borrowing.
Southern Water’s two annual reports run to 385 pages between them. They contain some proper improvements, a fair bit of corporate gloss and enough contradictory figures to make a calculator reach for the aspirin. So let’s begin where any story about a water company ought to begin: with the water.
Leakage fell — but more than a Bewl Water still slipped away
Southern Water reduced its annual leakage from 101.6 million litres a day in 2024/25 to 89.8 million litres in 2025/26. That’s a drop of 11.8 million litres a day, or about 11.6%. It’s a solid improvement and deserves to be recognised as such.
Translated out of water-industry gobbledegook, the daily saving is equivalent to about 4.7 Olympic-sized swimming pools. Across an average month, Southern Water saved roughly 144 pools; across the year, around 1,723. That annual saving — some 4.307 billion litres — amounts to nearly 13.9% of Bewl Water’s total capacity. The calculation uses 2.5 million litres for an Olympic-sized pool and Southern Water’s stated Bewl capacity of 31,000 megalitres, or 31 billion litres.

So far, so good.
The rub is what remained. At 89.8 million litres a day, Southern Water was still losing the equivalent of 35.9 Olympic pools every 24 hours, 1,093 pools in an average month and 13,111 pools across a 365-day year.
The annual loss comes to approximately 32.777 billion litres. Bewl Water holds 31 billion litres, meaning the reported leakage would fill the entire reservoir and leave enough water to fill another 5.7% of it. Put bluntly, more than one Bewl Water leaked away during the year.
There is an important qualification. Southern Water’s leakage measure includes losses from its own network and customer supply pipes. It isn’t saying every last drop escaped from a company-owned main. Even with that caveat, 89.8 million litres a day is still a ruddy great hole in the bucket.
The reporting around the improvement is unnecessarily muddled. The underlying performance table uses 101.6 million litres a day as the previous annual result. A performance summary instead says annual leakage fell from 101.1 to 89.8 million litres a day, apparently treating the previous rolling-average figure as though it were the annual comparator. Elsewhere, Southern Water says annual leakage fell from 100.7 to 89.8 million litres a day and that the three-year rolling average moved from a PR24 baseline of 105.4 to 101.1. Three different starting points are left bobbing about in the same report.
The underlying 101.6 figure is also the baseline Southern Water uses when describing its planned 34.7% leakage reduction by 2030. That makes it the clearest like-for-like annual comparator for the latest 89.8 result. The improvement survives the confusion; the reporting shouldn’t have created it in the first place.
Southern Water’s water-balance gap was separately rated red at 4.77%. That doesn’t cancel the leakage result, which was within the scope of independent limited assurance, but it does underline why the company needs to keep annual results, rolling averages and planning baselines in their proper boxes rather than tipping them all into the same paddling pool.

Pollution remains the filthy stain on the turnaround
Southern Water recorded 254 Category 1–3 wastewater pollution incidents during the year: one Category 1 incident, 11 Category 2 incidents and 242 Category 3 incidents. That was down from the Environment Agency’s figure of 269 incidents for calendar year 2024, so the total is heading in the right direction.
Serious pollution didn’t improve. Southern Water recorded 12 serious incidents, exactly the same number as the previous year. Its own annual report doesn’t try to put lipstick on that particular pig, admitting that “the level of serious pollutions remains unacceptable.”
Quite.
Those 12 incidents triggered an estimated performance penalty of £17.13 million. The wider pollution measure added another £14.06 million penalty. Between them, pollution performance put more than £31 million on the wrong side of the regulatory ledger before other rewards and penalties were taken into account.
Storm-overflow performance also missed its target. Southern Water reported an adjusted average of 21.11 spills per overflow, against a target of 17.99. The raw figures show 15,554 monitored spills across 977 overflows, with an additional adjustment for sites where monitoring coverage wasn’t complete.
There were also 149 dry-day pollution incidents in the underlying table. Dry-day spills are particularly awkward because there’s no biblical downpour to hide behind. When the weather’s dry, the usual corporate umbrella marked “exceptional rainfall” is of rather limited use.
The company says burst rising mains and blockages were the main causes of serious pollution. It has carried out end-to-end reviews of incidents and says it’s prioritising work at high-risk treatment sites. That may well bring improvement, but the starting line remains a long way from where customers and the environment have every right to expect it to be.
The Environment Agency’s latest completed annual assessment, covering calendar year 2024, awarded Southern Water two stars, meaning it “requires improvement”. The company has mostly been stuck on one or two stars since 2018, apart from no year in that period reaching three or four. Southern Water’s 2025/26 accounts forecast a possible one-star outcome for 2025, but that remains the company’s own expectation rather than the regulator’s final published verdict.
And the legal clouds haven’t blown over.
On 14 July 2026, Southern Water pleaded guilty to two environmental-permit offences concerning pollution of the River Test near Stockbridge. The Environment Agency had discovered a dark plume from the Fullerton wastewater treatment works in March 2023; suspended solids were more than three times the permitted limit and iron levels were also well above the allowed amount. Sentencing will take place later.
The regulator traced the pollution almost four miles upstream. Southern Water’s own site staff said only one of four tanks used to remove sludge and scum was working properly, while another had reportedly been awaiting repair for more than a year. Pumps serving the sand-bed filtration process were also having problems.
Southern Water didn’t alert the Environment Agency when it became aware of the problem or the equipment failures behind it. The company subsequently acknowledged that it had missed at least two opportunities to raise the alarm and that its procedures hadn’t been followed. That isn’t some distant relic from the era of fax machines and Filofaxes; it happened during the turnaround period Southern Water now presents as a clear break with the past.
Southern Water pleaded guilty at Medway Magistrates’ Court in April 2026 to 13 offences arising from sewage discharges at the Margate and Broadstairs wastewater pumping stations between 2019 and 2021. Nine charges concerned untreated sewage dumped off the Kent coast, three involved failures to notify the authorities promptly and within 24 hours, and the final offence concerned the absence of a standby pump at Margate between July 2019 and October 2020. Following a two-day sentencing hearing at Canterbury Crown Court, on Thursday & Friday of last week, Mr Justice Johnson imposed fines totalling £7,127,083. He said: “The harm was not confined to a single event, but arose from a pattern of repeated incidents over several years.” The judge said Southern Water’s 174 previous convictions showed a prolonged history of legal non-compliance and described that record as “an exceptionally serious aggravating factor”

