The UK’s water and wastewater system is “not fit for the current, let alone future, climate”, the Climate Change Committee (CCC) has concluded in A Well-Adapted UK, the Fourth Independent Assessment of UK Climate Risk (CCRA4-IA). Required every five years under the Climate Change Act, the report will inform the UK Government’s own Climate Change Risk Assessment, due before Parliament by January 2027.
The Committee identifies water-related impacts as central to three of the UK’s eight priority climate risks: damage and disruption from flooding, shortages from drought, and cascading impacts on infrastructure. By 2050, under 2°C of global warming, peak river flows could be up to 45% higher, last longer, and occur more frequently, while a public water supply shortfall of more than five billion litres a day is projected for England by 2055 in the absence of further action. A further annual shortfall averaging 320 million litres is projected for private supplies serving agriculture, industry, and power, rising to 657 million litres a year under a high-vulnerability scenario.
The report notes that water risks are not confined to the future. In April 2025, almost all of Scotland was placed on early warning of water scarcity. Parts of South East England remained in drought in January 2026 following a dry summer in 2025. In 2023, climate-driven warming and flooding at Lough Neagh, Northern Ireland, contributed to an unusually long and widespread harmful algal bloom that included toxic microalgae not previously recorded in Ireland. In England, 34.4% of water pumping stations and treatment works are currently at risk of flooding, rising to a projected 38.2% by 2040–2060.
Key adaptation actions for public and private water could cost around £1.2 billion a year, the Committee estimates
Leakage remains a major drag on resilience. In 2023 to 2024, 19% of the water put into supply in England was lost to leakage, around three-quarters of it from pipes owned by water utilities. The Committee estimates that more than 60% of England’s water deficit to 2055, and up to 80% over the next decade, will need to be met through demand and leakage reduction while new supply schemes are built. UK household water consumption remains higher than most comparable European countries, with Scotland recording the highest level at around 180 litres per person per day.
For the first time, the Committee proposes adaptation targets for the sector. By 2040, public water supply should be resilient to a 1-in-500-year drought, measured against future climate conditions; the existing standard in England and Wales would extend across the UK unless evidence shows it is not cost-effective in Scotland or Northern Ireland. Achieving this level of resilience by 2050 is estimated to cost £22.8–£26.6 billion (in 2025 prices), compared with £31.6–£50.6 billion if current standards are maintained and emergency measures relied upon for more severe droughts. By 2050, all water bodies should also meet sustainable abstraction criteria, and properties at risk of internal and external sewer flooding in a 1-in-50-year storm should have decreased.
Key adaptation actions for public and private water could cost around £1.2 billion a year (range £0.9–£2.6 billion, 2025 prices), the Committee estimates, while avoiding more expensive reactive measures. Reported benefit-cost ratios in the report include 1.8:1 for demand-side water efficiency measures, 2:1 for property-level rainwater harvesting (3:1 at the community level), 6:1 for upstream investment to reduce agricultural pollution, and 11:1 for water transfers and storage infrastructure (range 7:1–15:1 across English sub-regions). A national-scale package of cost-effective measures for private water users in agriculture, industry, and power could deliver £58.5 billion in benefits for £1.3 billion of investment, an overall benefit-cost ratio of 45:1.
On wastewater, the Committee warns that combined sewer systems will come under increasing strain as heavy rainfall intensifies
On wastewater, the Committee warns that combined sewer systems will come under increasing strain as heavy rainfall intensifies. Where heavy rain follows drought, overflows become more heavily contaminated, with greater health and environmental impacts. Without further action, the number of properties at risk of sewer flooding in a 1-in-50-year rainfall event in the Thames Valley alone is projected to rise by 31% between 2025 and 2050, from 315,600 to 414,300; Thames Water’s plan to protect them is expected to cost £20.5 billion over that period. The report cites the Thames Tideway Tunnel, which is reported to reduce combined sewer overflows by up to 95% in a typical year, and notes that public behavioural campaigns have cut blockages by as much as 60%.
The Committee identifies water and wastewater policy gaps that it considers urgent. UK-wide minimum water-efficiency standards for appliances and ‘flushability’ labelling do not yet exist, despite legislative proposals. It cites the United States, which introduced mandatory minimum standards in 1994 and saw a 22% decline in water use between 1999 and 2016, and Australia, whose Water Efficiency Labelling Scheme is reported to save 12.4 litres per person per day (rising to a projected 19.5 by 2036), with over 80% of consumers using the label when making purchases. Scottish Water estimates that 15% of the investment needed to meet drinking water quality standards from 2027 to 2033 is attributable to climate change.
More broadly, the report calls for around £11 billion a year in UK adaptation investment (range £7–£22 billion) to 2050, with cooling, flood preparedness and water management accounting for about two-thirds of the total. The Committee argues the existing national approach to adaptation is “not fit for purpose” and recommends meaningful objectives backed by targets, delivery plans with secured resources, monitoring against outcomes, and improved tools and skills. Responses now sit with the UK Government, the Northern Ireland Executive, and the Scottish and Welsh Governments, which are due to publish national adaptation plans after the formal risk assessment to Parliament.
