Southern Water cut the average minutes of supply lost per property by 96% in FY2025-26, which the regulators' joint report of October 2026 calls its "strongest-ever performance" on supply interruptions. In the same period the Environment Agency rated it 1 star for 2025, down from 2 stars in 2024.
The water side
The joint report puts drinking water compliance at 99.98% of tests in calendar 2025 and describes quality as "exceptional." Total leakage fell 8.1% in FY2025-26. The company's annual report gives supply interruptions of 00:05:01 for the year. The Drinking Water Inspectorate nevertheless lists 42 live improvement items for the company, with deadlines running to 2035.
The wastewater side
The Environment Agency counted 301 pollution incidents from Southern Water's sewerage and water supply assets in 2025, 12 of them serious. Its sewerage incident rate of 64 per 10,000 km of sewer was, in the agency's words, "the worst" in the sector. The rate had fallen from 110 in 2019 to 59 in 2023 before rising to 68 in 2024. In 2025, 96.7% of treatment works met numeric permit limits, with 11 sites failing.
What customers see
Internal sewer flooding rose 40% in FY2025-26, and Southern Water ranked 17th of 17 companies for customer satisfaction. In February 2026 Ofwat accepted undertakings that include £13.5 million of additional investment from the company and its shareholders for "the remaining failures it must address."
Where the wastewater weakness sits, how 929 environmental schemes due by March 2030 compare with year-one delivery of 50.0%, and which regulatory decisions come next are covered in the full report. The full report, Water Systems Overview: Southern Water, is available for USD 499. For a free overview, read the Southern Water Utility Snapshot.