The third route: Using extreme decentralization to create resilient urban water systems.

For much of the world's urban population, centralized treatment plants and pipe networks built in the nineteenth and twentieth centuries provide homes with water and a means of disposing of the resulting wastewater. Due to the real or perceived inability of existing systems to deliver safe and palatable water, many users apply additional treatment prior to consumption. Where piped water supply is lacking, drinking water is obtained through water vendors at considerable cost. Despite economic inefficiencies and public health risks inherent in these two water supply systems, the high sunk costs of existing water infrastructure along with low returns on investment and the inflexible nature of the institutions involved in water provision have slowed down the diffusion of alternative approaches that may prove to be less expensive, more adaptable and safer than the current system. We advocate a third, complementary route: household-based personalized water systems. Initially, relatively affluent people expecting more functionality and sustainability from water systems will invest in personalized water systems that allow them to tailor their water to their personal preferences. This approach will tap into the tremendous creativity-base of individual users and entrepreneurs, facilitating the type of co-creation that accelerated the rapid development of consumer electronics. Competition among manufacturers and economies of scale that accrue as these systems become more popular will lead to rapid innovation that drives down costs, improves performance and expands access. These solutions complement emerging approaches for sanitation and resource recovery that do not rely upon sewers for the management of human waste.