Thames Water's London water resource zone ended 2025-26 with a supply-demand balance of −17.43 Ml/d in dry year conditions. Its 2024 water resources plan had forecast a surplus of 62.58 Ml/d for the same year. The zone serves about 8.3 million people, and the shortfall came before the company imposed a company-wide hosepipe ban on July 23, 2026.
Leakage did most of the damage
London's distribution input was 1,953 Ml/d, 74 Ml/d above forecast. Leakage accounted for 53 Ml/d of that excess: 404 Ml/d against a planned 350 Ml/d. Across the company, dry year leakage reached 592.7 Ml/d against a forecast of 498.3 Ml/d, even though pressure management and mains replacement met their 2025-26 forecasts. Thames Water now says it is unlikely to meet its leakage forecast for the 2025–2030 period.
Supply went missing too
Water available for use in London was 45 Ml/d below forecast. The Gateway desalination plant had its deployable output cut from 25 Ml/d to zero because its membranes need replacing and no approved replacements are available; the company estimates 18 to 24 months for approval. With write-downs at three groundwater sites, London lost 43.3 Ml/d of deployable output in the year.
A study of the 2022 drought adds a deeper problem: the company was probably operating with about 180 Ml/d less deployable output on the Lower Thames than its plan assumed.
Why it matters now
London's resilience to emergency drought orders stands at 1 in 100 years, against a target of 1 in 200 in the 2030s. The schemes meant to close that gap, Teddington and White Horse Reservoir, are not due until the 2030s and 2040.
The report sets out how each zone's balance moved, which schemes are due before 2030 and what to watch in the revised plan tables. The full report, Climate Resilient Water Resources Management: Thames Water, is available for USD 499 at https://ourfuturewaterintelligence.com/reports/climate-resilient-water-resources-management-thames-water. For a free overview, read the Thames Water Utility Snapshot at https://ourfuturewaterintelligence.com/utilities/thames-water.