Background and context

Trends in urban water use are unsustainable in many locations, with high demand (social preferences) and leakage levels (institutional/economic failings, asset management challenges) coupled with climate impacts and pollution issues (environmental drivers). Population growth and urban expansion stress water resources. Combined with changes in supply characteristics, pressure is increasing on traditional resources. Alternative supplies offer the chance to use traditional sources more effectively, using alternative sources for other uses (watering parks, irrigation).

Alternative sources offer options during droughts and can mitigate flooding impacts. They enhance flexibility, relieving pressure on traditional sources and help mitigate development challenges. Alternative water supplies are increasingly being considered by national/municipal organisations to reduce pressure on traditional sources and to contribute to supply security. Applying alternative technologies to developing cities is a priority due to high expected growth rates and quite often a low, variable or unreliable water resource. This is a global issue, featuring in international discussions (e.g. IWA Cities of the Future Programme and the Rockefeller 100 Resilient Cities Initiative). Few studies quantify the contribution of alternative systems to increasing supply security. Our research contributes to filling this knowledge gap, especially in the context of developing cities in the global South and addresses a pressing global issue.