Provision of conventional centralised water, wastewater and stormwater systems for urban municipal services has been common practice for over 100 years. These systems center around the protection of human health, ensuring reliable water supply and minimizing flooding; often with minimal consideration of the environmental and ecological impacts associated with fresh water extraction and wastewater discharge. These urban water systems are facing unprecedented challenges in this century from the emerging issues of climate variability, population growth, aging infrastructure, urbanisation and resource constraints. In this context, the current level of urban water service provision can't be provided within the existing centralised system framework, unless there is a significant increase in investment, to enlarge and rehabilitate the existing centralized systems. Water service providers and managers are therefore considering alternative and sustainable means of providing water services in this environment. Decentralised and distributed water and wastewater systems, which are planned within an integrated water management concept, are being promoted either in combination with centralised systems; or alone as the sustainable solution for urban water servicing. Current urban water systems are beginning to undergo a transition, where decentralised systems will play a major role in the long-term sustainability of these systems to meet the above mentioned challenges. However, since decentralized systems are relatively new and involve increased complexity there are wide knowledge gaps in their planning, design, implementation, operation and management, which are impeding their uptake. This paper summarises the role of decentralized systems in the transitioning of centralised systems to a more sustainable state and discusses some of the complexities in the implementation of these systems.

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