Knowledge about sewer solids has advanced rapidly in the last few decades due to academic research triggered by an emerging renewed interest from sewer operators. It is now known that sewer solids are implicated in: loss of conveyance; potential for acute and chronic pollution of watercourses and effects inside sewers such as generation of malodorous gases and fabric corrosion. Despite this advance in knowledge, there is much that still needs to be understood, particularly the details of some of the mechanisms of flow-solids interactions, such as deposition, consolidation, erosion, biochemical interactions and processes. The history of knowledge development is outlined and areas where there is a need for further elucidation are highlighted.

The paper argues that the concept and practice of sustainability have proved too difficult to achieve within traditional water management, and there is a lack of political will to move towards truly sustainable water services. Instead, compromised concepts, including resistance, resilience, ecosystem services, natural capital and adaptation are defining approaches; each of which may contribute partially to sustainability. Pressures due to the changing climate, ecological degradation, human demands, urbanization and deteriorating assets are challenging sustainability and compelling changes to water management. Water is now seen less as a problem to be managed than as an opportunity, as wherever situated, water brings many opportunities to contribute to anthropogenic needs. New ideas are helping to frame the way in which water management is being approached: (i) waste is no longer waste, but a potential resource within a circular economy; (ii) the interconnectedness of infrastructure systems and services and circularity of the water cycle mean there is a need to integrate approaches; (iii) nature-based systems should be preferenced for water infrastructure. These issues and ideas are considered here, together with examples of schemes showing that managing flooding can lead to wider benefits, and potential longer-term sustainability. This article is part of the theme issue ‘Urban flood resilience’.

Green stormwater infrastructure (GSI) measures provide a wide range of benefits beyond simply dealing with stormwater. In the United Kingdom such measures are termed sustainable drainage systems (SuDS). There are a number of tools and procedures for assessing the benefits provided, some of which give a monetized bottom line. A U.K. project led by the Construction Industry Research and Information Association (CIRIA) has reviewed the available knowledge and techniques for valuing GSI and other benefits, and from this developed a new freely available valuation tool, known as the Benefits of SuDS Tool (BeST). This has been further developed to include spatial and temporal planning for the incremental implementation of a portfolio of SuDS over time and in extent. The tool is now being used in various countries for scenario planning to assist decision makers to explore future options and their relative robustness and flexibility over time. Case studies are presented from the United Kingdom and the Netherlands to illustrate the use of the tool and methods developed.