The new study suggests that a paradigm shift towards scaled decentralised systems is necessary to achieve sustainability and resilience in urban water infrastructure.

With cities globally experiencing enormous pressure to meet increasing water demands, handle extreme events, and minimise resource consumption and environmental impacts, the current model of centralised water infrastructure planning has been criticised as unsustainable. Urban water infrastructure refers to the water supply and wastewater collection systems and includes the treatment plants.

Most cities have centralised systems of urban water infrastructure. This implies, there would be one or a few sources of water that are treated centrally and then distributed through the water supply network. Similarly, the wastewater collection is also carried out and treated in large sewage treatment units at the outskirts of the city. These entail a centralised system of urban water infrastructure.

A recent study by researchers at the Indian Institute of Technology Bombay (IITB) argues that a paradigm shift towards scaled decentralised systems is necessary to achieve sustainability and resilience in urban water infrastructure (UWI). The research highlights the need to incorporate both sustainability and resilience perspectives in UWI life-cycles.

Raising concerns on the prevalent centralised systems, the authors of the research article, Prof Pradip Kalbar and Ms Shweta Lokhande from the Centre for Urban Science and Engineering (CUSE) at IIT Bombay, note that, “Centralised systems are most vulnerable to service hampering during failures or extreme events such as flooding. They lack the ability to cater to location-specific needs, for example, opportunities for recycling wastewater. Another prominent lacuna is the underutilised infrastructure resulting in inefficient operation of conveyance networks and treatment plants.”

They further add that “Large-scale centralised systems are associated with a lock-in period of investment, thereby preventing flexibility through innovations. Also, no benefits of scale of the economy are achieved beyond a particular scale, in fact, centralised systems substantially increase the burden on the environment through intensive energy and resource consumption.”

In other words, a primary concern with the prevalent UWI model is its linear, 'take-make-dispose' economy that relies on the frequent extraction of fresh water and dumps untreated water back into natural bodies. However, with growing resource scarcity and environmental concerns, this approach is no longer sustainable. The study proposes a shift towards a circular economy model that incorporates principles of reuse and recycling in water management.

Moreover, the study emphasises the importance of resilience in infrastructure planning to cope with increasing climate change-related stress and uncertainties associated with urbanisation. Large cities, which are most vulnerable to uncertainties, must adopt resilient UWI systems that can adapt to varying service levels during emergencies.

However, few existing studies approach UWI planning with a simultaneous emphasis on sustainability and resilience. Resilience in infrastructure is a relatively new addition to the sustainability perspective. Making infrastructure resilient calls for more investment. Therein lies the opportunity for a fundamental shift in how urban water management is approached - a move away from centralised systems towards decentralised UWI.

Emphasising this key shift, Prof Pradip Kalbar and Ms Shweta Lokhande note that, “It is critical to consider both sustainability and resilience aspects in planning urban water infrastructure as against mere techno-economic assessments. In addition, we suggest adopting an appropriate scale of implementing decentralised infrastructure which should be decided based on the scale of the city i.e. total sewage generated in a city.”

The centralised approach of UWI, which was conceived in the early 1900s, lacks the flexibility to cope with the changing dynamics of today's cities. Among the challenges are the complex coordination between various departments in a utility, risks related to critical route failures in extreme events, and the unsuitability of systems implemented in developed countries for use in developing ones.

The proposed alternative is a move towards so-called scaled decentralisation—systems that are neither highly centralised nor highly decentralised. Rather, the planning, implementation, and maintenance of UWI would be decentralised to an optimal level, depending on the specific context and conditions of a city. Potential benefits of scaled decentralisation include reduced life-cycle costs, lowered environmental impact, improved governance, increased resilience and enhanced recycling potential.

The shift towards scaled decentralised systems facilitates a circular approach to water management, encouraging the recycling of treated water and the creation of new water sources. It also increases the flexibility and adaptability of UWI, which is crucial for building resilience in the face of climate-related extreme events.

However, realising this paradigm shift requires a deep understanding of the factors that drive decentralisation, including technological innovation, environmental considerations, cost- effectiveness and governance capacities. Whether high-tech or low-tech, the suitability of a specific technology in a given context depends largely on the site conditions and scale of implementation.

In addition, Prof Pradip Kalbar and Ms Shweta Lokhande have identified the factors helping scaled decentralisation: One, awareness generation among decision-makers and urban local bodies regarding the multiple benefits of scaled decentralised systems. Two, decision support tools/ frameworks/ techniques for planners and engineers to implement scaled decentralisation. And three, paradigm shift in planning through capacity building of civil engineering students and planners (potential future consultants and decision makers) to approach urban water infrastructure through the lens of scaled decentralised systems. The researchers conclude that the overall strategy of UWI is more critical than specific technology choices. It advocates a move towards an optimal zone combining centralised and decentralised treatment systems to create resilient and sustainable urban water management systems. This approach would be beneficial for both developed and developing countries, helping to replace ageing UWI in the former and shape new infrastructure planning in the latter.

As the authors of this study emphasise, it is important for researchers, practitioners, and urban local bodies to work towards quantifying the economic scale of decentralisation, resulting in better optimization models, case studies and improved policymaking.