"Increasingly, water is available in the wrong place at the wrong time. Long dry periods are followed by intense rainfall that soils and drainage systems can barely absorb. Managing these extremes is becoming one of the key infrastructure challenges of our time," said Dr. Stephan Wasielewski, Head of Water Infrastructure at Drees & Sommer.

Drees & Sommer identifies five areas where cities and infrastructure operators can act. The first is retaining rainwater locally through infiltration areas, green roofs and cisterns. In Berlin, the firm supported the district of Lichtenberg in developing green and infiltration areas across around 135,000 sqm of sealed surfaces at schools, reducing runoff into the sewer network. The second area is reducing losses in ageing infrastructure using digital leak detection and AI-based forecasting tools to identify pipe failures before major leaks occur.

The third approach involves reusing water for irrigation, technical systems or industrial processes where drinking-water quality is not required. For Alzchem Group in southern Germany, Drees & Sommer is assessing how process water from the company's central wastewater treatment plant can be treated and reused within operations. The fourth area is improving transparency through digital tools and registers such as Ireland's national Water Abstraction Register. The fifth is expanding green infrastructure in cities to allow water infiltration and reduce urban heat, as demonstrated by a landscape concept developed for the 27-hectare Telegrafenberg campus in Potsdam, where around 78% of trees have already been affected by heat and drought.

"What matters now is how quickly cities and municipalities prepare for changing climate conditions and increasing pressure on water resources," said Wasielewski. While households can contribute through rain barrels and water-saving fixtures, Drees & Sommer argues that the greatest impact will come from investment in infrastructure, stormwater management and water reuse systems.