In the world of construction, what levers can help reduce pressure on water resources? T. M.: Materials and design play a key role in reducing pressure on water resources, particularly through use of equipment that limits consumption. Digital tools, such as smart meters and real-time monitoring, can further reinforce water savings. Updating building codes to require water-efficient solutions in new build and major renovations can lead to long-term savings. Cities can go further by directly incorporating water reuse into planning regulations, for example by recycling gray water or harvesting rainwater where possible. At the start of your career, you worked on the concept of the “compact city”, specifically on optimizing the land footprint of buildings and infrastructure. Do you think this concept could be beneficial for water resource management? T. M.: Yes. Optimizing water infrastructure in more densely populated areas reduces the risk of leaks and losses in the networks, and denser forms of housing create economies of scale that make gray water reuse or shared rainwater harvesting systems more viable. Limiting urban sprawl also frees up space for parks and nature-based solutions, which are essential for replenishing groundwater and mitigating water stress. Several cities, particularly in Asia and Europe, are experimenting with gray water management and decentralized collection systems. Based on your experience in Japan and at the OECD, what are the political or economic barriers that still slow down the adoption of these solutions? T. M.: Decentralized systems face economic barriers (equipment and maintenance costs), social barriers (negative perception of gray water), and institutional barriers (complex planning laws and governance). Integrated planning, clear protocols, and structured reporting are essential for their widespread adoption. VIEWPOINT TADASHI MATSUMOTO Head of Unit, National Urban Policy and Climate Resilience Cities, Urban Policy, and Sustainable Development Division, OECD READ the full interview in Constructing a Sustainable Future “ By 2050, nearly one in two city dwellers could be short of water. Already, a quarter of the world’s population is experiencing high water stress. ” “Water stress: a systemic approach is essential” 121
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