2026 Water Cycle White Paper | Chapter 4FY2026 Water Cycle White Paper: Promoting Effective Water Use

The chapter, “Promoting Proper and Effective Use of Water, and Related Measures,” covers securing safe, high-quality water; sustainable water and sewerage services; responses to severe drought; disaster response; maintenance and renewal of water infrastructure; efficient water use; the water environment and ecosystems; waterside spaces; water culture; and responses to global warming. It describes government measures in fiscal 2025 concerning water supply and sewerage, agricultural water use, rivers, forests, and groundwater.

The background includes population decline and aging facilities, as well as changes in low-rainfall and heavy-rain events associated with climate change. The white paper explains challenges concerning water supply security, disaster response, and facility management, and calls for information sharing and cooperation among the national government, local governments, water users, businesses, and residents.

The chapter treats the water cycle as connecting forests, rivers, farmland, cities, lakes and marshes, and coastal areas, linking water quantity and quality management with ecosystem conservation. It describes cross-sector measures including infrastructure development and inspection, institutional and technical support, use of rainwater, reclaimed water, and groundwater, and use of nature’s purification and storage functions.

Through measures such as introducing advanced treatment technologies, including ozone treatment, and improving water quality management, the population affected by unpleasant tastes and odors such as musty odors declined from about 22 million in FY1990 to around 3 million in FY2024.

In a sewer pipe damage accident in Yashio, Saitama Prefecture, in January 2025, one truck was caught up in the incident, the driver died, and about 1.2 million people were asked to limit sewer use. Heavy rains from August 2025 caused damage to homes, river flooding, and landslides, while water outages at water facilities affected up to 42,343 households.

Following low rainfall and high temperatures in 2025, measures included adjusting agricultural water distribution, arranging pumps and water trucks, and subsidizing expenses; rice crops grew generally well.

To secure safe, high-quality water, water utilities and others were encouraged to develop Water Safety Plans or carry out equivalent hazard management, advancing integrated risk management from water sources to taps. Measures also included regulating factory wastewater; ensuring compliance with and inspection of standards to prevent subsurface infiltration; managing soil contamination and pesticides; and compiling and publishing notifications under the PRTR system. Research and information provision on PFOS and PFOA were advanced, and in December 2025 utilities were asked to conduct tests and other measures in line with water quality standards. Ahead of the addition of these substances to the standards on April 1, 2026, examples of responses, including reducing concentrations when provisional target values are exceeded, were provided.

Measures to strengthen water and sewerage infrastructure included facility reorganization, public-private partnerships, digital transformation, integrated operations by multiple local governments, combinations of centralized and decentralized systems that take regional conditions and disaster recovery into account, and energy efficiency. The government provided subsidies for costs of considering Water PPP implementation and for facility rehabilitation and renewal, supported information exchange between public and private sectors, and implemented a Meister system that draws on staff expertise. A review panel issued its second compilation in January 2026 and is considering policy directions with 2050 in view.

Drought measures included assessing water supply security and risks, promoting systems for stakeholder information sharing, and developing drought response timelines. Basic plans for water resources development were revised from a demand-led approach to risk management. As of the end of March 2026, six river systems and five plans had been completed, while work on the Kiso River system began in November 2025. In FY2025, timelines for 10 additional river systems were published, bringing the total to 42. Other measures included establishing drought response headquarters, publishing conditions on a portal, arranging pumps and water trucks, and subsidizing emergency costs.

Flood and landslide measures included developing rivers, dams, and erosion control facilities; conducting advance releases from dams; and improving basin storage and infiltration functions. The government also promoted use of hazard maps and personal timelines, supported evacuation systems at facilities used by people requiring special consideration, and provided information. Measures included advance releases from agricultural dams, paddy field dams, rainwater storage in irrigation ponds, and drainage facility development, while prefecture-level information on linear rain bands continued. Preparations were made to put new disaster prevention weather information into operation from the 2026 flood season.

To maintain water supply and drainage functions during large-scale disasters, measures included seismic retrofitting, water transfers between systems, storage facilities, networks of wastewater treatment facilities, mutual assistance, emergency water supply, business continuity plans, and use of alternative water sources such as groundwater. In FY2025, TEC-FORCE personnel were dispatched for 17 disasters, totaling about 3,000 person-days. Measures also included seismic retrofit plans informed by the Noto Peninsula Earthquake, revisions to recovery procedures and manuals, and use of mobile water purification facilities.

To address aging infrastructure, maintenance and management are being advanced through individual facility plans, inspections and repairs, renewal, consolidation and closure, and regional integration. Measures used include asset management under the Water Supply Act, sewerage maintenance and repair standards, and guidelines for renewal, seismic retrofitting, and asset management of industrial waterworks. As of March 2025, about 95% of water utilities and others had established mapping systems. As of FY2023, more than half of core agricultural water facilities had exceeded their standard service life.

To use water efficiently, measures included preventing leaks, remote monitoring and control of agricultural water facilities, and ICT-based water management. The government also developed rainwater use facilities and promoted public awareness, used reclaimed water for miscellaneous and agricultural purposes, and disseminated water-saving information. Water environment measures included domestic wastewater treatment, wastewater regulations, groundwater contamination countermeasures, purification and dredging, and nitrogen and phosphorus management in enclosed coastal waters. The river BOD environmental standard attainment rate remained around 95%, while the lake COD attainment rate was generally about 50% to 60%.

Ecosystem measures included surveys and monitoring of rivers, lakes, marshes, wetlands, and coastal areas; invasive species control; nature restoration; migratory bird conservation; and support for local activities. Nature Coexistence Sites, which certify areas where private-sector and other activities take place, totaled 569 sites as of March 2026. Waterside measures advanced river town development, spring water conservation, and water-friendly facilities. Water culture measures supported development in water source areas, upstream-downstream exchanges, and activities to pass on local history and agricultural water heritage.

Responses to global warming included introducing renewable energy, improving energy efficiency, developing forests as carbon sinks, and adapting to droughts and floods. Support covered hydropower and small hydropower, improved dam operations, floating solar power, and energy and fertilizer use of sewage sludge. Measures also included river development based on climate change, flood protection, water quality monitoring, and agricultural water management, as well as consideration of assessments of climate change impacts on water resources and water quality.